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Liu T, Pyle AM. Highly Reactive Group I Introns Ubiquitous in Pathogenic Fungi. J Mol Biol 2024; 436:168513. [PMID: 38447889 DOI: 10.1016/j.jmb.2024.168513] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2024] [Revised: 02/25/2024] [Accepted: 02/27/2024] [Indexed: 03/08/2024]
Abstract
Systemic fungal infections are a growing public health threat, and yet viable antifungal drug targets are limited as fungi share a similar proteome with humans. However, features of RNA metabolism and the noncoding transcriptomes in fungi are distinctive. For example, fungi harbor highly structured RNA elements that humans lack, such as self-splicing introns within key housekeeping genes in the mitochondria. However, the location and function of these mitochondrial riboregulatory elements has largely eluded characterization. Here we used an RNA-structure-based bioinformatics pipeline to identify the group I introns interrupting key mitochondrial genes in medically relevant fungi, revealing their fixation within a handful of genetic hotspots and their ubiquitous presence across divergent phylogenies of fungi, including all highest priority pathogens such as Candida albicans, Candida auris, Aspergillus fumigatus and Cryptococcus neoformans. We then biochemically characterized two representative introns from C. albicans and C. auris, demonstrating their exceptionally efficient splicing catalysis relative to previously-characterized group I introns. Indeed, the C. albicans mitochondrial intron displays extremely rapid catalytic turnover, even at ambient temperatures and physiological magnesium ion concentrations. Our results unmask a significant new set of players in the RNA metabolism of pathogenic fungi, suggesting a promising new type of antifungal drug target.
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Affiliation(s)
- Tianshuo Liu
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520, USA
| | - Anna Marie Pyle
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520, USA; Department of Chemistry, Yale University, New Haven, CT 06520, USA; Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA.
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2
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Gao W, Yang A, Rivas E. Thirteen dubious ways to detect conserved structural RNAs. IUBMB Life 2023; 75:471-492. [PMID: 36495545 PMCID: PMC11234323 DOI: 10.1002/iub.2694] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Accepted: 10/24/2022] [Indexed: 12/14/2022]
Abstract
Covariation induced by compensatory base substitutions in RNA alignments is a great way to deduce conserved RNA structure, in principle. In practice, success depends on many factors, importantly the quality and depth of the alignment and the choice of covariation statistic. Measuring covariation between pairs of aligned positions is easy. However, using covariation to infer evolutionarily conserved RNA structure is complicated by other extraneous sources of covariation such as that resulting from homologous sequences having evolved from a common ancestor. In order to provide evidence of evolutionarily conserved RNA structure, a method to distinguish covariation due to sources other than RNA structure is necessary. Moreover, there are several sorts of artifactually generated covariation signals that can further confound the analysis. Additionally, some covariation signal is difficult to detect due to incomplete comparative data. Here, we investigate and critically discuss the practice of inferring conserved RNA structure by comparative sequence analysis. We provide new methods on how to approach and decide which of the numerous long non-coding RNAs (lncRNAs) have biologically relevant structures.
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Affiliation(s)
- William Gao
- Department of Genetics, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Ann Yang
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA
| | - Elena Rivas
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA
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Yang H, Chen H, Ni Y, Li J, Cai Y, Wang J, Liu C. Mitochondrial Genome Sequence of Salvia officinalis (Lamiales: Lamiaceae) Suggests Diverse Genome Structures in Cogeneric Species and Finds the Stop Gain of Genes through RNA Editing Events. Int J Mol Sci 2023; 24:ijms24065372. [PMID: 36982448 PMCID: PMC10048906 DOI: 10.3390/ijms24065372] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 02/20/2023] [Accepted: 03/02/2023] [Indexed: 03/14/2023] Open
Abstract
Our previous study was the first to confirm that the predominant conformation of mitochondrial genome (mitogenome) sequence of Salvia species contains two circular chromosomes. To further understand the organization, variation, and evolution of Salvia mitogenomes, we characterized the mitogenome of Salvia officinalis. The mitogenome of S. officinalis was sequenced using Illumina short reads and Nanopore long reads and assembled using a hybrid assembly strategy. We found that the predominant conformation of the S. officinalis mitogenome also had two circular chromosomes that were 268,341 bp (MC1) and 39,827 bp (MC2) in length. The S. officinalis mitogenome encoded an angiosperm-typical set of 24 core genes, 9 variable genes, 3 rRNA genes, and 16 tRNA genes. We found many rearrangements of the Salvia mitogenome through inter- and intra-specific comparisons. A phylogenetic analysis of the coding sequences (CDs) of 26 common protein-coding genes (PCGs) of 11 Lamiales species and 2 outgroup taxa strongly indicated that the S. officinalis was a sister taxon to S. miltiorrhiza, consistent with the results obtained using concatenated CDs of common plastid genes. The mapping of RNA-seq data to the CDs of PCGs led to the identification of 451 C-to-U RNA editing sites from 31 PCGs of the S. officinalis mitogenome. Using PCR amplification and Sanger sequencing methods, we successfully validated 113 of the 126 RNA editing sites from 11 PCGs. The results of this study suggest that the predominant conformation of the S. officinalis mitogenome are two circular chromosomes, and the stop gain of rpl5 was found through RNA editing events of the Salvia mitogenome.
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Affiliation(s)
- Heyu Yang
- School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China
- Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing 100193, China
| | - Haimei Chen
- Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing 100193, China
| | - Yang Ni
- Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing 100193, China
| | - Jingling Li
- Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing 100193, China
| | - Yisha Cai
- Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing 100193, China
| | - Jiehua Wang
- School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China
- Correspondence: (J.W.); (C.L.); Tel.: +86-022-8740-2072 (J.W.); +86-10-5783-3111 (C.L.); Fax: +86-022-2740-7956 (J.W.); +86-10-62899715 (C.L.)
| | - Chang Liu
- Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing 100193, China
- Correspondence: (J.W.); (C.L.); Tel.: +86-022-8740-2072 (J.W.); +86-10-5783-3111 (C.L.); Fax: +86-022-2740-7956 (J.W.); +86-10-62899715 (C.L.)
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4
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Lian K, Furulund BMN, Tveita AA, Haugen P, Johansen SD. Mobile group I introns at nuclear rDNA position L2066 harbor sense and antisense homing endonuclease genes intervened by spliceosomal introns. Mob DNA 2022; 13:23. [PMID: 36209098 PMCID: PMC9548176 DOI: 10.1186/s13100-022-00280-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Accepted: 09/28/2022] [Indexed: 11/24/2022] Open
Abstract
Background Mobile group I introns encode homing endonucleases that confer intron mobility initiated by a double-strand break in the intron-lacking allele at the site of insertion. Nuclear ribosomal DNA of some fungi and protists contain mobile group I introns harboring His-Cys homing endonuclease genes (HEGs). An intriguing question is how protein-coding genes embedded in nuclear ribosomal DNA become expressed. To address this gap of knowledge we analyzed nuclear L2066 group I introns from myxomycetes and ascomycetes. Results A total of 34 introns were investigated, including two identified mobile-type introns in myxomycetes with HEGs oriented in sense or antisense directions. Intriguingly, both HEGs are interrupted by spliceosomal introns. The intron in Didymium squamulosum, which harbors an antisense oriented HEG, was investigated in more detail. The group I intron RNA self-splices in vitro, thus generating ligated exons and full-length intron circles. The intron HEG is expressed in vivo in Didymium cells, which involves removal of a 47-nt spliceosomal intron (I-47) and 3′ polyadenylation of the mRNA. The D. squamulosum HEG (lacking the I-47 intron) was over-expressed in E. coli, and the corresponding protein was purified and shown to confer endonuclease activity. The homing endonuclease was shown to cleave an intron-lacking DNA and to produce a pentanucleotide 3′ overhang at the intron insertion site. Conclusions The L2066 family of nuclear group I introns all belong to the group IE subclass. The D. squamulosum L2066 intron contains major hallmarks of a true mobile group I intron by encoding a His-Cys homing endonuclease that generates a double-strand break at the DNA insertion site. We propose a potential model to explain how an antisense HEG becomes expressed from a nuclear ribosomal DNA locus. Supplementary Information The online version contains supplementary material available at 10.1186/s13100-022-00280-4.
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Affiliation(s)
- Kjersti Lian
- Nofima AS, Muninbakken 9-13, Breivika, 9291, Tromsø, Norway
| | - Betty M N Furulund
- Genomics division, Faculty of Biosciences and Aquaculture, Nord University, N-8049, Bodø, Norway
| | - Anders A Tveita
- Medical Department, Bærum Hospital, Vestre Viken Hospital Trulst, Drammen, Norway
| | - Peik Haugen
- Department of Chemistry and Center for Bioinformatics, Faculty of Science and Technology, UiT-The Arctic University of Norway, N-9037, Tromsø, Norway
| | - Steinar D Johansen
- Genomics division, Faculty of Biosciences and Aquaculture, Nord University, N-8049, Bodø, Norway.
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Structural Organization of S516 Group I Introns in Myxomycetes. Genes (Basel) 2022; 13:genes13060944. [PMID: 35741706 PMCID: PMC9223047 DOI: 10.3390/genes13060944] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2022] [Revised: 05/21/2022] [Accepted: 05/23/2022] [Indexed: 02/04/2023] Open
Abstract
Group I introns are mobile genetic elements encoding self-splicing ribozymes. Group I introns in nuclear genes are restricted to ribosomal DNA of eukaryotic microorganisms. For example, the myxomycetes, which represent a distinct protist phylum with a unique life strategy, are rich in nucleolar group I introns. We analyzed and compared 75 group I introns at position 516 in the small subunit ribosomal DNA from diverse and distantly related myxomycete taxa. A consensus secondary structure revealed a conserved group IC1 ribozyme core, but with a surprising RNA sequence complexity in the peripheral regions. Five S516 group I introns possess a twintron organization, where a His-Cys homing endonuclease gene insertion was interrupted by a small spliceosomal intron. Eleven S516 introns contained direct repeat arrays with varying lengths of the repeated motif, a varying copy number, and different structural organizations. Phylogenetic analyses of S516 introns and the corresponding host genes revealed a complex inheritance pattern, with both vertical and horizontal transfers. Finally, we reconstructed the evolutionary history of S516 nucleolar group I introns from insertion of mobile-type introns at unoccupied cognate sites, through homing endonuclease gene degradation and loss, and finally to the complete loss of introns. We conclude that myxomycete S516 introns represent a family of genetic elements with surprisingly dynamic structures despite a common function in RNA self-splicing.
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Thompson SRL, Lee DK, Lachance MA, Smith DR. Mutational Effects of Mobile Introns on the Mitochondrial Genomes of Metschnikowia Yeasts. Front Genet 2021; 12:785218. [PMID: 34804133 PMCID: PMC8601654 DOI: 10.3389/fgene.2021.785218] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Accepted: 10/19/2021] [Indexed: 11/25/2022] Open
Abstract
It has been argued that DNA repair by homologous recombination in the context of endonuclease-mediated cleavage can cause mutations. To better understand this phenomenon, we examined homologous recombination following endonuclease cleavage in a native genomic context: the movement of self-splicing introns in the mitochondrial genomes of Metschnikowia yeasts. Self-splicing mitochondrial introns are mobile elements, which can copy and paste themselves at specific insertion sites in mitochondrial DNA using a homing endonuclease in conjunction with homologous recombination. Here, we explore the mutational effects of self-splicing introns by comparing sequence variation within the intron-rich cox1 and cob genes from 71 strains (belonging to 40 species) from the yeast genus Metschnikowia. We observed a higher density of single nucleotide polymorphisms around self-splicing-intron insertion sites. Given what is currently known about the movement of organelle introns, it is likely that their mutational effects result from the high binding affinity of endonucleases and their interference with repair machinery during homologous recombination (or, alternatively, via gene conversion occurring during the intron insertion process). These findings suggest that there are fitness costs to harbouring self-splicing, mobile introns and will help us better understand the risks associated with modern biotechnologies that use endonuclease-mediated homologous recombination, such as CRISPR-Cas9 gene editing.
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Affiliation(s)
- Scout R L Thompson
- Department of Biology, University of Western Ontario, London, ON, Canada
| | - Dong Kyung Lee
- Department of Biology, University of Western Ontario, London, ON, Canada
| | | | - David Roy Smith
- Department of Biology, University of Western Ontario, London, ON, Canada
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Patinios C, Creutzburg SCA, Arifah AQ, Adiego-Pérez B, Gyimah E, Ingham C, Kengen SWM, van der Oost J, Staals RHJ. Streamlined CRISPR genome engineering in wild-type bacteria using SIBR-Cas. Nucleic Acids Res 2021; 49:11392-11404. [PMID: 34614191 PMCID: PMC8565351 DOI: 10.1093/nar/gkab893] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Revised: 09/16/2021] [Accepted: 09/20/2021] [Indexed: 11/13/2022] Open
Abstract
CRISPR-Cas is a powerful tool for genome editing in bacteria. However, its efficacy is dependent on host factors (such as DNA repair pathways) and/or exogenous expression of recombinases. In this study, we mitigated these constraints by developing a simple and widely applicable genome engineering tool for bacteria which we termed SIBR-Cas (Self-splicing Intron-Based Riboswitch-Cas). SIBR-Cas was generated from a mutant library of the theophylline-dependent self-splicing T4 td intron that allows for tight and inducible control over CRISPR-Cas counter-selection. This control delays CRISPR-Cas counter-selection, granting more time for the editing event (e.g. by homologous recombination) to occur. Without the use of exogenous recombinases, SIBR-Cas was successfully applied to knock-out several genes in three wild-type bacteria species (Escherichia coli MG1655, Pseudomonas putida KT2440 and Flavobacterium IR1) with poor homologous recombination systems. Compared to other genome engineering tools, SIBR-Cas is simple, tightly regulated and widely applicable for most (non-model) bacteria. Furthermore, we propose that SIBR can have a wider application as a simple gene expression and gene regulation control mechanism for any gene or RNA of interest in bacteria.
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Affiliation(s)
- Constantinos Patinios
- Laboratory of Microbiology, Wageningen University and Research, Stippeneng 4, 6708 WE, Wageningen, The Netherlands
| | - Sjoerd C A Creutzburg
- Laboratory of Microbiology, Wageningen University and Research, Stippeneng 4, 6708 WE, Wageningen, The Netherlands
| | - Adini Q Arifah
- Laboratory of Microbiology, Wageningen University and Research, Stippeneng 4, 6708 WE, Wageningen, The Netherlands
| | - Belén Adiego-Pérez
- Laboratory of Microbiology, Wageningen University and Research, Stippeneng 4, 6708 WE, Wageningen, The Netherlands
| | - Evans A Gyimah
- Laboratory of Microbiology, Wageningen University and Research, Stippeneng 4, 6708 WE, Wageningen, The Netherlands
| | - Colin J Ingham
- Hoekmine Besloten Vennootschap, Kenniscentrum Technologie en Innovatie, Hogeschool Utrecht, 3584 CS, Utrecht, The Netherlands
| | - Servé W M Kengen
- Laboratory of Microbiology, Wageningen University and Research, Stippeneng 4, 6708 WE, Wageningen, The Netherlands
| | - John van der Oost
- Laboratory of Microbiology, Wageningen University and Research, Stippeneng 4, 6708 WE, Wageningen, The Netherlands
| | - Raymond H J Staals
- Laboratory of Microbiology, Wageningen University and Research, Stippeneng 4, 6708 WE, Wageningen, The Netherlands
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A Phylogenetic Approach to Structural Variation in Organization of Nuclear Group I Introns and Their Ribozymes. Noncoding RNA 2021; 7:ncrna7030043. [PMID: 34449660 PMCID: PMC8395846 DOI: 10.3390/ncrna7030043] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Revised: 07/16/2021] [Accepted: 07/21/2021] [Indexed: 01/22/2023] Open
Abstract
Nuclear group I introns are restricted to the ribosomal DNA locus where they interrupt genes for small subunit and large subunit ribosomal RNAs at conserved sites in some eukaryotic microorganisms. Here, the myxomycete protists are a frequent source of nuclear group I introns due to their unique life strategy and a billion years of separate evolution. The ribosomal DNA of the myxomycete Mucilago crustacea was investigated and found to contain seven group I introns, including a direct repeat-containing intron at insertion site S1389 in the small subunit ribosomal RNA gene. We collected, analyzed, and compared 72 S1389 group IC1 introns representing diverse myxomycete taxa. The consensus secondary structure revealed a conserved ribozyme core, but with surprising sequence variations in the guanosine binding site in segment P7. Some S1389 introns harbored large extension sequences in the peripheral region of segment P9 containing direct repeat arrays. These repeats contained up to 52 copies of a putative internal guide sequence motif. Other S1389 introns harbored homing endonuclease genes in segment P1 encoding His-Cys proteins. Homing endonuclease genes were further interrupted by small spliceosomal introns that have to be removed in order to generate the open reading frames. Phylogenetic analyses of S1389 intron and host gene indicated both vertical and horizontal intron transfer during evolution, and revealed sporadic appearances of direct repeats, homing endonuclease genes, and guanosine binding site variants among the myxomycete taxa.
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Megarioti AH, Kouvelis VN. The Coevolution of Fungal Mitochondrial Introns and Their Homing Endonucleases (GIY-YIG and LAGLIDADG). Genome Biol Evol 2021; 12:1337-1354. [PMID: 32585032 PMCID: PMC7487136 DOI: 10.1093/gbe/evaa126] [Citation(s) in RCA: 40] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/17/2020] [Indexed: 12/21/2022] Open
Abstract
Fungal mitochondrial (mt) genomes exhibit great diversity in size which is partially attributed to their variable intergenic regions and most importantly to the inclusion of introns within their genes. These introns belong to group I or II, and both of them are self-splicing. The majority of them carry genes encoding homing endonucleases, either LAGLIDADG or GIY-YIG. In this study, it was found that these intronic homing endonucleases genes (HEGs) may originate from mt free-standing open reading frames which can be found nowadays in species belonging to Early Diverging Fungi as “living fossils.” A total of 487 introns carrying HEGs which were located in the publicly available mt genomes of representative species belonging to orders from all fungal phyla was analyzed. Their distribution in the mt genes, their insertion target sequence, and the phylogenetic analyses of the HEGs showed that these introns along with their HEGs form a composite structure in which both selfish elements coevolved. The invasion of the ancestral free-standing HEGs in the introns occurred through a perpetual mechanism, called in this study as “aenaon” hypothesis. It is based on recombination, transpositions, and horizontal gene transfer events throughout evolution. HEGs phylogenetically clustered primarily according to their intron hosts and secondarily to the mt genes carrying the introns and their HEGs. The evolutionary models created revealed an “intron-early” evolution which was enriched by “intron-late” events through many different independent recombinational events which resulted from both vertical and horizontal gene transfers.
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Affiliation(s)
- Amalia H Megarioti
- Department of Genetics and Biotechnology, Faculty of Biology, National and Kapodistrian University of Athens, Greece
| | - Vassili N Kouvelis
- Department of Genetics and Biotechnology, Faculty of Biology, National and Kapodistrian University of Athens, Greece
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Mayers CG, Harrington TC, Wai A, Hausner G. Recent and Ongoing Horizontal Transfer of Mitochondrial Introns Between Two Fungal Tree Pathogens. Front Microbiol 2021; 12:656609. [PMID: 34149643 PMCID: PMC8208691 DOI: 10.3389/fmicb.2021.656609] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2021] [Accepted: 04/09/2021] [Indexed: 11/23/2022] Open
Abstract
Two recently introduced fungal plant pathogens (Ceratocystis lukuohia and Ceratocystis huliohia) are responsible for Rapid ‘ōhi‘a Death (ROD) in Hawai‘i. Despite being sexually incompatible, the two pathogens often co-occur in diseased ‘ōhi‘a sapwood, where genetic interaction is possible. We sequenced and annotated 33 mitochondrial genomes of the two pathogens and related species, and investigated 35 total Ceratocystis mitogenomes. Ten mtDNA regions [one group I intron, seven group II introns, and two autonomous homing endonuclease (HE) genes] were heterogeneously present in C. lukuohia mitogenomes, which were otherwise identical. Molecular surveys with specific primers showed that the 10 regions had uneven geographic distribution amongst populations of C. lukuohia. Conversely, identical orthologs of each region were present in every studied isolate of C. huliohia regardless of geographical origin. Close relatives of C. lukuohia lacked or, rarely, had few and dissimilar orthologs of the 10 regions, whereas most relatives of C. huliohia had identical or nearly identical orthologs. Each region included or worked in tandem with HE genes or reverse transcriptase/maturases that could facilitate interspecific horizontal transfers from intron-minus to intron-plus alleles. These results suggest that the 10 regions originated in C. huliohia and are actively moving to populations of C. lukuohia, perhaps through transient cytoplasmic contact of hyphal tips (anastomosis) in the wound surface of ‘ōhi‘a trees. Such contact would allow for the transfer of mitochondria followed by mitochondrial fusion or cytoplasmic exchange of intron intermediaries, which suggests that further genomic interaction may also exist between the two pathogens.
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Affiliation(s)
- Chase G Mayers
- Department of Plant Pathology and Microbiology, Iowa State University, Ames, IA, United States
| | - Thomas C Harrington
- Department of Plant Pathology and Microbiology, Iowa State University, Ames, IA, United States
| | - Alvan Wai
- Department of Microbiology, University of Manitoba, Winnipeg, MB, Canada
| | - Georg Hausner
- Department of Microbiology, University of Manitoba, Winnipeg, MB, Canada
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11
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Rausch JW, Heinz WF, Payea MJ, Sherpa C, Gorospe M, Le Grice SFJ. Characterizing and circumventing sequence restrictions for synthesis of circular RNA in vitro. Nucleic Acids Res 2021; 49:e35. [PMID: 33406226 DOI: 10.1093/nar/gkaa1256] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2020] [Revised: 11/27/2020] [Accepted: 12/18/2020] [Indexed: 01/10/2023] Open
Abstract
Just as eukaryotic circular RNA (circRNA) is a product of intracellular backsplicing, custom circRNA can be synthesized in vitro using a transcription template in which transposed halves of a split group I intron flank the sequence of the RNA to be circularized. Such permuted intron-exon (PIE) constructs have been used to produce circRNA versions of ribozymes, mimics of viral RNA motifs, a streptavidin aptamer, and protein expression vectors for genetic engineering and vaccine development. One limitation of this approach is the obligatory incorporation of small RNA segments (E1 and E2) into nascent circRNA at the site of end-joining. This restriction may preclude synthesis of small circRNA therapeutics and RNA nanoparticles that are sensitive to extraneous sequence, as well as larger circRNA mimics whose sequences must precisely match those of the native species on which they are modelled. In this work, we used serial mutagenesis and in vitro selection to determine how varying E1 and E2 sequences in a thymidylate synthase (td) group I intron PIE transcription template construct affects circRNA synthesis yield. Based on our collective findings, we present guidelines for the design of custom-tailored PIE transcription templates from which synthetic circRNAs of almost any sequence may be efficiently synthesized.
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Affiliation(s)
- Jason W Rausch
- Basic Research Laboratory, National Cancer Institute, NIH, Frederick, MD 21702, USA
| | - William F Heinz
- Optical Microscopy and Analysis Laboratory, Cancer Research Technology Program, Frederick National Laboratory for Cancer Research, Frederick, MD 21702, USA
| | - Matthew J Payea
- Laboratory of Genetics and Genomics, National Institute on Aging-Intramural Research Program, National Institutes of Health, Baltimore, MD 21224, USA
| | - Chringma Sherpa
- Basic Research Laboratory, National Cancer Institute, NIH, Frederick, MD 21702, USA
| | - Myriam Gorospe
- Laboratory of Genetics and Genomics, National Institute on Aging-Intramural Research Program, National Institutes of Health, Baltimore, MD 21224, USA
| | - Stuart F J Le Grice
- Basic Research Laboratory, National Cancer Institute, NIH, Frederick, MD 21702, USA
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The Mitochondrial Genome of the Sea Anemone Stichodactyla haddoni Reveals Catalytic Introns, Insertion-Like Element, and Unexpected Phylogeny. Life (Basel) 2021; 11:life11050402. [PMID: 33924866 PMCID: PMC8146996 DOI: 10.3390/life11050402] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Revised: 04/21/2021] [Accepted: 04/26/2021] [Indexed: 01/15/2023] Open
Abstract
A hallmark of sea anemone mitochondrial genomes (mitogenomes) is the presence of complex catalytic group I introns. Here, we report the complete mitogenome and corresponding transcriptome of the carpet sea anemone Stichodactyla haddoni (family Stichodactylidae). The mitogenome is vertebrate-like in size, organization, and gene content. Two mitochondrial genes encoding NADH dehydrogenase subunit 5 (ND5) and cytochrome c oxidase subunit I (COI) are interrupted with complex group I introns, and one of the introns (ND5-717) harbors two conventional mitochondrial genes (ND1 and ND3) within its sequence. All the mitochondrial genes, including the group I introns, are expressed at the RNA level. Nonconventional and optional mitochondrial genes are present in the mitogenome of S. haddoni. One of these gene codes for a COI-884 intron homing endonuclease and is organized in-frame with the upstream COI exon. The insertion-like orfA is expressed as RNA and translocated in the mitogenome as compared with other sea anemones. Phylogenetic analyses based on complete nucleotide and derived protein sequences indicate that S. haddoni is embedded within the family Actiniidae, a finding that challenges current taxonomy.
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Corsaro D, Venditti D. Putative group I introns in the eukaryote nuclear internal transcribed spacers. Curr Genet 2019; 66:373-384. [PMID: 31463775 DOI: 10.1007/s00294-019-01027-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2019] [Revised: 08/05/2019] [Accepted: 08/17/2019] [Indexed: 11/28/2022]
Abstract
Group I introns are mobile genetic elements that interrupt genes encoding proteins and RNAs. In the rRNA operon, introns can insert in the small subunit (SSU) and large subunit (LSU) of a wide variety of protists and various prokaryotes, but they were never found in the ITS region. In this study, unusually long ITS regions of fungi and closely related unicellular organisms (Polychytrium aggregatum, Mitosporidium daphniae, Amoeboaphelidium occidentale and Nuclearia simplex) were analysed. While the insertion of repeats is responsible for long ITS in other eukaryotes, the increased size of the sequences analysed herein seems rather due to the presence of introns in ITS-1 or ITS-2. The identified insertions can be folded in secondary structures according to group I intron models, and they cluster within introns in conserved core-based phylogeny. In addition, for Mitosporidium, Amoeboaphelidium and Nuclearia, more conventional ITS-2 structures can be deduced once spacer introns are removed. Sequences of five shark species were also analysed for their structure and included in phylogeny because of unpublished work reporting introns in their ITS, obtaining congruent results. Overall, the data presented herein indicate that spacer regions may contain introns.
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Affiliation(s)
- Daniele Corsaro
- CHLAREAS, 12 rue du Maconnais, Vandoeuvre-lès-Nancy, 54500, France.
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14
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Nawrocki EP, Jones TA, Eddy SR. Group I introns are widespread in archaea. Nucleic Acids Res 2019; 46:7970-7976. [PMID: 29788499 PMCID: PMC6125680 DOI: 10.1093/nar/gky414] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2018] [Accepted: 05/04/2018] [Indexed: 01/28/2023] Open
Abstract
Group I catalytic introns have been found in bacterial, viral, organellar, and some eukaryotic genomes, but not in archaea. All known archaeal introns are bulge-helix-bulge (BHB) introns, with the exception of a few group II introns. It has been proposed that BHB introns arose from extinct group I intron ancestors, much like eukaryotic spliceosomal introns are thought to have descended from group II introns. However, group I introns have little sequence conservation, making them difficult to detect with standard sequence similarity searches. Taking advantage of recent improvements in a computational homology search method that accounts for both conserved sequence and RNA secondary structure, we have identified 39 group I introns in a wide range of archaeal phyla, including examples of group I introns and BHB introns in the same host gene.
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Affiliation(s)
- Eric P Nawrocki
- National Center for Biotechnology Information, U.S. National Library of Medicine, Bethesda, MD 20894, USA
| | - Thomas A Jones
- Howard Hughes Medical Institute, Harvard University, Cambridge, USA.,Department of Molecular and Cellular Biology, Harvard University, Cambridge, USA
| | - Sean R Eddy
- Howard Hughes Medical Institute, Harvard University, Cambridge, USA.,Department of Molecular and Cellular Biology, Harvard University, Cambridge, USA.,School of Engineering and Applied Sciences, Harvard University, Cambridge, USA
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15
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Chi SI, Dahl M, Emblem Å, Johansen SD. Giant group I intron in a mitochondrial genome is removed by RNA back-splicing. BMC Mol Biol 2019; 20:16. [PMID: 31153363 PMCID: PMC6545197 DOI: 10.1186/s12867-019-0134-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Accepted: 05/23/2019] [Indexed: 01/29/2023] Open
Abstract
Background The mitochondrial genomes of mushroom corals (Corallimorpharia) are remarkable for harboring two complex group I introns; ND5-717 and COI-884. How these autocatalytic RNA elements interfere with mitochondrial RNA processing is currently not known. Here, we report experimental support for unconventional processing events of ND5-717 containing RNA. Results We obtained the complete mitochondrial genome sequences and corresponding mitochondrial transcriptomes of the two distantly related corallimorpharian species Ricordea yuma and Amplexidiscus fenestrafer. All mitochondrial genes were found to be expressed at the RNA-level. Both introns were perfectly removed by autocatalytic splicing, but COI-884 excision appeared more efficient than ND5-717. ND5-717 was organized into giant group I intron elements of 18.1 kb and 19.3 kb in A. fenestrafer and R. yuma, respectively. The intron harbored almost the entire mitochondrial genome embedded within the P8 peripheral segment. Conclusion ND5-717 was removed by group I intron splicing from a small primary transcript that contained a permutated intron–exon arrangement. The splicing pathway involved a circular exon-containing RNA intermediate, which is a hallmark of RNA back-splicing. ND5-717 represents the first reported natural group I intron that becomes excised by back-splicing from a permuted precursor RNA. Back-splicing may explain why Corallimorpharia mitochondrial genomes tolerate giant group I introns. Electronic supplementary material The online version of this article (10.1186/s12867-019-0134-y) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Sylvia Ighem Chi
- Department of Medical Biology, Faculty of Health Sciences, UiT-The Arctic University of Norway, Tromsø, Norway
| | - Mikael Dahl
- Department of Medical Biology, Faculty of Health Sciences, UiT-The Arctic University of Norway, Tromsø, Norway
| | - Åse Emblem
- Department of Medical Biology, Faculty of Health Sciences, UiT-The Arctic University of Norway, Tromsø, Norway
| | - Steinar D Johansen
- Department of Medical Biology, Faculty of Health Sciences, UiT-The Arctic University of Norway, Tromsø, Norway. .,Genomics Group, Faculty of Biosciences and Aquaculture, Nord University, Bodø, Norway.
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16
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Kishor R, Sharma GJ. The use of the hypervariable P8 region of trnL(UAA) intron for identification of orchid species: Evidence from restriction site polymorphism analysis. PLoS One 2018; 13:e0196680. [PMID: 29718976 PMCID: PMC5931654 DOI: 10.1371/journal.pone.0196680] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2018] [Accepted: 04/17/2018] [Indexed: 11/18/2022] Open
Abstract
The P8 stem-loop region of the trnL intron, which is known to be hypervariable in size with multiple repeat motifs and created difficulties in alignment, is always excluded in phylogenetic as well as barcode analyses. This region was investigated for species discrimination in 98 taxa of orchids belonging to the tribe Vandeae using in silico mapping of restriction site polymorphism. The length of the P8 regions varied from 200 nucleotides in Aerides rosea to 669 nucleotides in Dendrophylax sallei. Forty two taxa had unique lengths, while as many as eight shared a common length of 521 nucleotides. Of the 35 restriction endonucleases producing digestions in the P8 regions, three, viz., AgsI, ApoI and TspDTI turned out to have recognition sites across all the 98 taxa being studied. When their restriction data were combined, 92 taxa could be discriminated leaving three taxon pairs. However, Acampe papillosa and Aeranthes arachnites despite having similar restriction sites differed in their P8 lengths. This is the first report on thorough investigation of the P8 region of trnL intron for search of species specific restriction sites and hence its use as a potential plant DNA barcode.
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Affiliation(s)
- Rajkumar Kishor
- Department of Life Sciences, Manipur University, Imphal, Manipur, India
- * E-mail:
| | - G. J. Sharma
- Department of Life Sciences, Manipur University, Imphal, Manipur, India
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17
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Smith LG, Zhao J, Mathews DH, Turner DH. Physics-based all-atom modeling of RNA energetics and structure. WILEY INTERDISCIPLINARY REVIEWS-RNA 2018; 8. [PMID: 28815951 DOI: 10.1002/wrna.1422] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Revised: 02/03/2017] [Accepted: 03/08/2017] [Indexed: 12/31/2022]
Abstract
The database of RNA sequences is exploding, but knowledge of energetics, structures, and dynamics lags behind. All-atom computational methods, such as molecular dynamics, hold promise for closing this gap. New algorithms and faster computers have accelerated progress in improving the reliability and accuracy of predictions. Currently, the methods can facilitate refinement of experimentally determined nuclear magnetic resonance and x-ray structures, but are 'unreliable' for predictions based only on sequence. Much remains to be discovered, however, about the many molecular interactions driving RNA folding and the best way to approximate them quantitatively. The large number of parameters required means that a wide variety of experimental results will be required to benchmark force fields and different approaches. As computational methods become more reliable and accessible, they will be used by an increasing number of biologists, much as x-ray crystallography has expanded. Thus, many fundamental physical principles underlying the computational methods are described. This review presents a summary of the current state of molecular dynamics as applied to RNA. It is designed to be helpful to students, postdoctoral fellows, and faculty who are considering or starting computational studies of RNA. WIREs RNA 2017, 8:e1422. doi: 10.1002/wrna.1422.
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Affiliation(s)
- Louis G Smith
- Department of Biochemistry and Biophysics and Center for RNA Biology, School of Medicine and Dentistry, University of Rochester, Rochester, NY, USA
| | - Jianbo Zhao
- Department of Chemistry and Center for RNA Biology, University of Rochester, Rochester, NY, USA
| | - David H Mathews
- Department of Biochemistry and Biophysics and Center for RNA Biology, School of Medicine and Dentistry, University of Rochester, Rochester, NY, USA
| | - Douglas H Turner
- Department of Chemistry and Center for RNA Biology, University of Rochester, Rochester, NY, USA
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18
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Gomes FEES, Arantes TD, Fernandes JAL, Ferreira LC, Romero H, Bosco SMG, Oliveira MTB, Del Negro GMB, Theodoro RC. Polymorphism in Mitochondrial Group I Introns among Cryptococcus neoformans and Cryptococcus gattii Genotypes and Its Association with Drug Susceptibility. Front Microbiol 2018; 9:86. [PMID: 29467729 PMCID: PMC5808193 DOI: 10.3389/fmicb.2018.00086] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2017] [Accepted: 01/12/2018] [Indexed: 12/21/2022] Open
Abstract
Cryptococcosis, one of the most important systemic mycosis in the world, is caused by different genotypes of Cryptococcus neoformans and Cryptococcus gattii, which differ in their ecology, epidemiology, and antifungal susceptibility. Therefore, the search for new molecular markers for genotyping, pathogenicity and drug susceptibility is necessary. Group I introns fulfill the requisites for such task because (i) they are polymorphic sequences; (ii) their self-splicing is inhibited by some drugs; and (iii) their correct splicing under parasitic conditions is indispensable for pathogen survival. Here, we investigated the presence of group I introns in the mitochondrial LSU rRNA gene in 77 Cryptococcus isolates and its possible relation to drug susceptibility. Sequencing revealed two new introns in the LSU rRNA gene. All the introns showed high sequence similarity to other mitochondrial introns from distinct fungi, supporting the hypothesis of an ancient non-allelic invasion. Intron presence was statistically associated with those genotypes reported to be less pathogenic (p < 0.001). Further virulence assays are needed to confirm this finding. In addition, in vitro antifungal tests indicated that the presence of LSU rRNA introns may influence the minimum inhibitory concentration (MIC) of amphotericin B and 5-fluorocytosine. These findings point to group I introns in the mitochondrial genome of Cryptococcus as potential molecular markers for antifungal resistance, as well as therapeutic targets.
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Affiliation(s)
- Felipe E. E. S. Gomes
- Department of Biochemistry, Universidade Federal do Rio Grande do Norte, Natal, Brazil
- Institute of Tropical Medicine of Rio Grande do Norte, Universidade Federal do Rio Grande do Norte, Natal, Brazil
| | - Thales D. Arantes
- Department of Biochemistry, Universidade Federal do Rio Grande do Norte, Natal, Brazil
- Institute of Tropical Medicine of Rio Grande do Norte, Universidade Federal do Rio Grande do Norte, Natal, Brazil
| | - José A. L. Fernandes
- Institute of Tropical Medicine of Rio Grande do Norte, Universidade Federal do Rio Grande do Norte, Natal, Brazil
| | - Leonardo C. Ferreira
- Department of Biochemistry, Universidade Federal do Rio Grande do Norte, Natal, Brazil
- Institute of Tropical Medicine of Rio Grande do Norte, Universidade Federal do Rio Grande do Norte, Natal, Brazil
| | - Héctor Romero
- Laboratorio de Organizacion y Evolución del Genoma/Unidad de Genómica Evolutiva, Departamento de Ecología y Evolución, Facultad de Ciencias/CURE, Universidad de la República, Maldonado, Uruguay
| | - Sandra M. G. Bosco
- Department of Microbiology and Immunology, Institute of Biosciences, Universidade Estadual Paulista Julio de Mesquita Filho, São Paulo, Brazil
| | - Maria T. B. Oliveira
- Department of Microbiology and Parasitology, Universidade Federal do Rio Grande do Norte, Natal, Brazil
| | - Gilda M. B. Del Negro
- Institute of Tropical Medicine of São Paulo, Universidade de São Paulo, São Paulo, Brazil
| | - Raquel C. Theodoro
- Institute of Tropical Medicine of Rio Grande do Norte, Universidade Federal do Rio Grande do Norte, Natal, Brazil
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19
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Guha TK, Wai A, Mullineux ST, Hausner G. The intron landscape of the mtDNA cytb gene among the Ascomycota: introns and intron-encoded open reading frames. Mitochondrial DNA A DNA Mapp Seq Anal 2017; 29:1015-1024. [DOI: 10.1080/24701394.2017.1404042] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Tuhin K. Guha
- Department of Microbiology, University of Manitoba, Winnipeg, Canada
| | - Alvan Wai
- Department of Microbiology, University of Manitoba, Winnipeg, Canada
| | | | - Georg Hausner
- Department of Microbiology, University of Manitoba, Winnipeg, Canada
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20
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Evolutionary and biogeographical implications of degraded LAGLIDADG endonuclease functionality and group I intron occurrence in stony corals (Scleractinia) and mushroom corals (Corallimorpharia). PLoS One 2017; 12:e0173734. [PMID: 28278261 PMCID: PMC5344465 DOI: 10.1371/journal.pone.0173734] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Accepted: 02/24/2017] [Indexed: 11/29/2022] Open
Abstract
Group I introns and homing endonuclease genes (HEGs) are mobile genetic elements, capable of invading target sequences in intron-less genomes. LAGLIDADG HEGs are the largest family of endonucleases, playing a key role in the mobility of group I introns in a process known as ‘homing’. Group I introns and HEGs are rare in metazoans, and can be mainly found inserted in the COXI gene of some sponges and cnidarians, including stony corals (Scleractinia) and mushroom corals (Corallimorpharia). Vertical and horizontal intron transfer mechanisms have been proposed as explanations for intron occurrence in cnidarians. However, the central role of LAGLIDADG motifs in intron mobility mechanisms remains poorly understood. To resolve questions regarding the evolutionary origin and distribution of group I introns and HEGs in Scleractinia and Corallimorpharia, we examined intron/HEGs sequences within a comprehensive phylogenetic framework. Analyses of LAGLIDADG motif conservation showed a high degree of degradation in complex Scleractinia and Corallimorpharia. Moreover, the two motifs lack the respective acidic residues necessary for metal-ion binding and catalysis, potentially impairing horizontal intron mobility. In contrast, both motifs are highly conserved within robust Scleractinia, indicating a fully functional endonuclease capable of promoting horizontal intron transference. A higher rate of non-synonymous substitutions (Ka) detected in the HEGs of complex Scleractinia and Corallimorpharia suggests degradation of the HEG, whereas lower Ka rates in robust Scleractinia are consistent with a scenario of purifying selection. Molecular-clock analyses and ancestral inference of intron type indicated an earlier intron insertion in complex Scleractinia and Corallimorpharia in comparison to robust Scleractinia. These findings suggest that the lack of horizontal intron transfers in the former two groups is related to an age-dependent degradation of the endonuclease activity. Moreover, they also explain the peculiar geographical patterns of introns in stony and mushroom corals.
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21
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Adams GC, Surve-Iyer RS, Iezzoni AF. Ribosomal DNA sequence divergence and group I introns within theLeucostomaspeciesL. cinctum,L. persoonii, andL. parapersooniisp. nov., ascomycetes that cause Cytospora canker of fruit trees. Mycologia 2017. [DOI: 10.1080/15572536.2003.11833153] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
| | - Rupa S. Surve-Iyer
- Department of Plant Pathology, Michigan State University, East Lansing, Michigan 48824-1312
| | - Amy F. Iezzoni
- Department of Horticulture, Michigan State University, East Lansing, Michigan 48824-1312
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22
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Design and Experimental Evolution of trans-Splicing Group I Intron Ribozymes. Molecules 2017; 22:molecules22010075. [PMID: 28045452 PMCID: PMC6155759 DOI: 10.3390/molecules22010075] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Revised: 12/27/2016] [Accepted: 12/29/2016] [Indexed: 12/31/2022] Open
Abstract
Group I intron ribozymes occur naturally as cis-splicing ribozymes, in the form of introns that do not require the spliceosome for their removal. Instead, they catalyze two consecutive trans-phosphorylation reactions to remove themselves from a primary transcript, and join the two flanking exons. Designed, trans-splicing variants of these ribozymes replace the 3′-portion of a substrate with the ribozyme’s 3′-exon, replace the 5′-portion with the ribozyme’s 5′-exon, or insert/remove an internal sequence of the substrate. Two of these designs have been evolved experimentally in cells, leading to variants of group I intron ribozymes that splice more efficiently, recruit a cellular protein to modify the substrate’s gene expression, or elucidate evolutionary pathways of ribozymes in cells. Some of the artificial, trans-splicing ribozymes are promising as tools in therapy, and as model systems for RNA evolution in cells. This review provides an overview of the different types of trans-splicing group I intron ribozymes that have been generated, and the experimental evolution systems that have been used to improve them.
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23
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Grewe F, Zhu A, Mower JP. Loss of a Trans-Splicing nad1 Intron from Geraniaceae and Transfer of the Maturase Gene matR to the Nucleus in Pelargonium. Genome Biol Evol 2016; 8:3193-3201. [PMID: 27664178 PMCID: PMC5174742 DOI: 10.1093/gbe/evw233] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The mitochondrial nad1 gene of seed plants has a complex structure, including four introns in cis or trans configurations and a maturase gene (matR) hosted within the final intron. In the geranium family (Geraniaceae), however, sequencing of representative species revealed that three of the four introns, including one in a trans configuration and another that hosts matR, were lost from the nad1 gene in their common ancestor. Despite the loss of the host intron, matR has been retained as a freestanding gene in most genera of the family, indicating that this maturase has additional functions beyond the splicing of its host intron. In the common ancestor of Pelargonium, matR was transferred to the nuclear genome, where it was split into two unlinked genes that encode either its reverse transcriptase or maturase domain. Both nuclear genes are transcribed and contain predicted mitochondrial targeting signals, suggesting that they express functional proteins that are imported into mitochondria. The nuclear localization and split domain structure of matR in the Pelargonium nuclear genome offers a unique opportunity to assess the function of these two domains using transgenic approaches.
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Affiliation(s)
- Felix Grewe
- Center for Plant Science Innovation, University of Nebraska, Lincoln, Nebraska.,Department of Agronomy and Horticulture, University of Nebraska, Lincoln, Nebraska.,Integrative Research Center, The Field Museum of Natural History, Chicago, Illinois
| | - Andan Zhu
- Center for Plant Science Innovation, University of Nebraska, Lincoln, Nebraska.,Department of Agronomy and Horticulture, University of Nebraska, Lincoln, Nebraska
| | - Jeffrey P Mower
- Center for Plant Science Innovation, University of Nebraska, Lincoln, Nebraska .,Department of Agronomy and Horticulture, University of Nebraska, Lincoln, Nebraska
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Abstract
Introns inserted within introns are commonly referred to as twintrons, however the original definition for twintron implied that splicing of the external member of the twintron could only proceed upon splicing of the internal member. This review examines the various types of twintron-like arrangements that have been reported and assigns them to either nested or twintron categories that are subdivided further into subtypes based on differences of their mode of splicing. Twintron-like arrangements evolved independently by fortuitous events among different types of introns but once formed they offer opportunities for the evolution of new regulatory strategies and/or novel genetic elements.
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Affiliation(s)
- Mohamed Hafez
- a Department of Biochemistry ; Faculty of Medicine; University of Montreal ; Montréal , QC Canada.,b Department of Botany and Microbiology ; Faculty of Science; Suez University ; Suez , Egypt
| | - Georg Hausner
- c Department of Microbiology ; University of Manitoba ; Winnipeg , MB Canada
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25
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Deng Y, Zhang Q, Ming R, Lin L, Lin X, Lin Y, Li X, Xie B, Wen Z. Analysis of the Mitochondrial Genome in Hypomyces aurantius Reveals a Novel Twintron Complex in Fungi. Int J Mol Sci 2016; 17:ijms17071049. [PMID: 27376282 PMCID: PMC4964425 DOI: 10.3390/ijms17071049] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Revised: 06/23/2016] [Accepted: 06/24/2016] [Indexed: 12/29/2022] Open
Abstract
Hypomyces aurantius is a mycoparasite that causes cobweb disease, a most serious disease of cultivated mushrooms. Intra-species identification is vital for disease control, however the lack of genomic data makes development of molecular markers challenging. Small size, high copy number, and high mutation rate of fungal mitochondrial genome makes it a good candidate for intra and inter species differentiation. In this study, the mitochondrial genome of H. H.a0001 was determined from genomic DNA using Illumina sequencing. The roughly 72 kb genome shows all major features found in other Hypocreales: 14 common protein genes, large and small subunit rRNAs genes and 27 tRNAs genes. Gene arrangement comparison showed conserved gene orders in Hypocreales mitochondria are relatively conserved, with the exception of Acremonium chrysogenum and Acremonium implicatum. Mitochondrial genome comparison also revealed that intron length primarily contributes to mitogenome size variation. Seventeen introns were detected in six conserved genes: five in cox1, four in rnl, three in cob, two each in atp6 and cox3, and one in cox2. Four introns were found to contain two introns or open reading frames: cox3-i2 is a twintron containing two group IA type introns; cox2-i1 is a group IB intron encoding two homing endonucleases; and cox1-i4 and cox1-i3 both contain two open reading frame (ORFs). Analyses combining secondary intronic structures, insertion sites, and similarities of homing endonuclease genes reveal two group IA introns arranged side by side within cox3-i2. Mitochondrial data for H. aurantius provides the basis for further studies relating to population genetics and species identification.
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Affiliation(s)
- Youjin Deng
- Mycological Research Center, College of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
- Center for Genomics and Biotechnology, Haixia Institute of Science and Technology, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
| | - Qihui Zhang
- Gutian Edible Fungal Research and Development Center, Ningde 352200, China.
| | - Ray Ming
- Gutian Edible Fungal Research and Development Center, Ningde 352200, China.
| | - Longji Lin
- Mycological Research Center, College of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
| | - Xiangzhi Lin
- Mycological Research Center, College of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
| | - Yiying Lin
- Mycological Research Center, College of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
| | - Xiao Li
- Mycological Research Center, College of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
| | - Baogui Xie
- Mycological Research Center, College of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
| | - Zhiqiang Wen
- Mycological Research Center, College of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
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26
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Masuda M, Hirose N, Ishikawa T, Ikawa Y, Nishimura K. Prototheca miyajii sp. nov., isolated from a patient with systemic protothecosis. Int J Syst Evol Microbiol 2016; 66:1510-1520. [DOI: 10.1099/ijsem.0.000911] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Affiliation(s)
- Michiaki Masuda
- Department of Microbiology, Dokkyo Medical University School of Medicine, Tochigi 321-0293, Japan
| | - Noriyuki Hirose
- Department of Microbiology, Dokkyo Medical University School of Medicine, Tochigi 321-0293, Japan
- BD Japan, Co., Ltd, Tokyo 107-0052, Japan
| | - Tomohiro Ishikawa
- Department of Microbiology, Dokkyo Medical University School of Medicine, Tochigi 321-0293, Japan
| | - Yoshiya Ikawa
- Laboratory of Biofunctional Chemistry, Department of Chemistry, Graduate School of Science and Engineering, University of Toyama, Toyama 930-8555, Japan
| | - Kazuko Nishimura
- Department of Microbiology, Dokkyo Medical University School of Medicine, Tochigi 321-0293, Japan
- First Laboratories, Co. Ltd, Kanagawa 211-0013, Japan
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27
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Huchon D, Szitenberg A, Shefer S, Ilan M, Feldstein T. Mitochondrial group I and group II introns in the sponge orders Agelasida and Axinellida. BMC Evol Biol 2015; 15:278. [PMID: 26653218 PMCID: PMC4676843 DOI: 10.1186/s12862-015-0556-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2015] [Accepted: 12/03/2015] [Indexed: 11/21/2022] Open
Abstract
Background Self-splicing introns are present in the mitochondria of members of most eukaryotic lineages. They are divided into Group I and Group II introns, according to their secondary structure and splicing mechanism. Being rare in animals, self-splicing introns were only described in a few sponges, cnidarians, placozoans and one annelid species. In sponges, three types of mitochondrial Group I introns were previously described in two demosponge families (Tetillidae, and Aplysinellidae) and in the homoscleromorph family Plakinidae. These three introns differ in their insertion site, secondary structure and in the sequence of the LAGLIDADG gene they encode. Notably, no group II introns have been previously described in sponges. Results We report here the presence of mitochondrial introns in the cytochrome oxidase subunit 1 (COI) gene of three additional sponge species from three different families: Agelas oroides (Agelasidae, Agelasida), Cymbaxinellapverrucosa (Hymerhabdiidae, Agelasida) and Axinella polypoides (Axinellidae, Axinellida). We show, for the first time, that sponges can also harbour Group II introns in their COI gene, whose presence in animals’ mitochondria has so far been described in only two phyla, Placozoa and Annelida. Surprisingly, two different Group II introns were discovered in the COI gene of C. verrucosa. Phylogenetic analysis indicates that the Group II introns present in C. verrucosa are related to red algae (Rhodophyta) introns. Conclusions The differences found among intron secondary structures and the phylogenetic inferences support the hypothesis that the introns originated from independent horizontal gene transfer events. Our results thus suggest that self-splicing introns are more diverse in the mitochondrial genome of sponges than previously anticipated. Electronic supplementary material The online version of this article (doi:10.1186/s12862-015-0556-1) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Dorothée Huchon
- Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, 6997801, Israel. .,The Steinhardt Museum of Natural History, Israel National Center for Biodiversity Studies, Tel Aviv University, Tel Aviv, 6997801, Israel.
| | - Amir Szitenberg
- Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, 6997801, Israel. .,Current address: School of Biological, Biomedical and Environmental Sciences, University of Hull, Hull, HU6 7RX, UK.
| | - Sigal Shefer
- Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, 6997801, Israel. .,The Steinhardt Museum of Natural History, Israel National Center for Biodiversity Studies, Tel Aviv University, Tel Aviv, 6997801, Israel.
| | - Micha Ilan
- Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, 6997801, Israel.
| | - Tamar Feldstein
- Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, 6997801, Israel. .,The Steinhardt Museum of Natural History, Israel National Center for Biodiversity Studies, Tel Aviv University, Tel Aviv, 6997801, Israel.
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28
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Abstract
Phenotypic capacitance refers to the ability of a genome to accumulate mutations that are conditionally hidden and only reveal phenotype-altering effects after certain environmental or genetic changes. Capacitance has important implications for the evolution of novel forms and functions, but experimentally studied mechanisms behind capacitance are mostly limited to complex, multicomponent systems often involving several interacting protein molecules. Here we demonstrate phenotypic capacitance within a much simpler system, an individual RNA molecule with catalytic activity (ribozyme). This naturally occurring RNA molecule has a modular structure, where a scaffold module acts as an intramolecular chaperone that facilitates folding of a second catalytic module. Previous studies have shown that the scaffold module is not absolutely required for activity, but dramatically decreases the concentration of magnesium ions required for the formation of an active site. Here, we use an experimental perturbation of magnesium ion concentration that disrupts the folding of certain genetic variants of this ribozyme and use in vitro selection followed by deep sequencing to identify genotypes with altered phenotypes (catalytic activity). We identify multiple conditional mutations that alter the wild-type ribozyme phenotype under a stressful environmental condition of low magnesium ion concentration, but preserve the phenotype under more relaxed conditions. This conditional buffering is confined to the scaffold module, but controls the catalytic phenotype, demonstrating how modularity can enable phenotypic capacitance within a single macromolecule. RNA's ancient role in life suggests that phenotypic capacitance may have influenced evolution since life's origins.
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29
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Kaasalainen U, Olsson S, Rikkinen J. Evolution of the tRNALeu (UAA) Intron and Congruence of Genetic Markers in Lichen-Symbiotic Nostoc. PLoS One 2015; 10:e0131223. [PMID: 26098760 PMCID: PMC4476775 DOI: 10.1371/journal.pone.0131223] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Accepted: 05/29/2015] [Indexed: 01/16/2023] Open
Abstract
The group I intron interrupting the tRNALeu UAA gene (trnL) is present in most cyanobacterial genomes as well as in the plastids of many eukaryotic algae and all green plants. In lichen symbiotic Nostoc, the P6b stem-loop of trnL intron always involves one of two different repeat motifs, either Class I or Class II, both with unresolved evolutionary histories. Here we attempt to resolve the complex evolution of the two different trnL P6b region types. Our analysis indicates that the Class II repeat motif most likely appeared first and that independent and unidirectional shifts to the Class I motif have since taken place repeatedly. In addition, we compare our results with those obtained with other genetic markers and find strong evidence of recombination in the 16S rRNA gene, a marker widely used in phylogenetic studies on Bacteria. The congruence of the different genetic markers is successfully evaluated with the recently published software Saguaro, which has not previously been utilized in comparable studies.
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Affiliation(s)
- Ulla Kaasalainen
- Department of Geobiology, University of Göttingen, Göttingen, Germany
- * E-mail:
| | - Sanna Olsson
- Department of Biosciences, University of Helsinki, Helsinki, Finland
| | - Jouko Rikkinen
- Department of Biosciences, University of Helsinki, Helsinki, Finland
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30
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Sowa SW, Vazquez-Anderson J, Clark CA, De La Peña R, Dunn K, Fung EK, Khoury MJ, Contreras LM. Exploiting post-transcriptional regulation to probe RNA structures in vivo via fluorescence. Nucleic Acids Res 2014; 43:e13. [PMID: 25416800 PMCID: PMC4333371 DOI: 10.1093/nar/gku1191] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
While RNA structures have been extensively characterized in vitro, very few techniques exist to probe RNA structures inside cells. Here, we have exploited mechanisms of post-transcriptional regulation to synthesize fluorescence-based probes that assay RNA structures in vivo. Our probing system involves the co-expression of two constructs: (i) a target RNA and (ii) a reporter containing a probe complementary to a region in the target RNA attached to an RBS-sequestering hairpin and fused to a sequence encoding the green fluorescent protein (GFP). When a region of the target RNA is accessible, the area can interact with its complementary probe, resulting in fluorescence. By using this system, we observed varied patterns of structural accessibility along the length of the Tetrahymena group I intron. We performed in vivo DMS footprinting which, along with previous footprinting studies, helped to explain our probing results. Additionally, this novel approach represents a valuable tool to differentiate between RNA variants and to detect structural changes caused by subtle mutations. Our results capture some differences from traditional footprinting assays that could suggest that probing in vivo via oligonucleotide hybridization facilitates the detection of folding intermediates. Importantly, our data indicate that intracellular oligonucleotide probing can be a powerful complement to existing RNA structural probing methods.
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Affiliation(s)
- Steven W Sowa
- Microbiology Graduate Program, University of Texas at Austin, 100 E. 24th Street, A6500, Austin, TX 78712, USA
| | - Jorge Vazquez-Anderson
- McKetta Department of Chemical Engineering, University of Texas at Austin, 200 E. Dean Keeton St., Stop C0400, Austin, TX 78712, USA
| | - Chelsea A Clark
- McKetta Department of Chemical Engineering, University of Texas at Austin, 200 E. Dean Keeton St., Stop C0400, Austin, TX 78712, USA
| | - Ricardo De La Peña
- McKetta Department of Chemical Engineering, University of Texas at Austin, 200 E. Dean Keeton St., Stop C0400, Austin, TX 78712, USA
| | - Kaitlin Dunn
- McKetta Department of Chemical Engineering, University of Texas at Austin, 200 E. Dean Keeton St., Stop C0400, Austin, TX 78712, USA
| | - Emily K Fung
- McKetta Department of Chemical Engineering, University of Texas at Austin, 200 E. Dean Keeton St., Stop C0400, Austin, TX 78712, USA
| | - Mark J Khoury
- McKetta Department of Chemical Engineering, University of Texas at Austin, 200 E. Dean Keeton St., Stop C0400, Austin, TX 78712, USA
| | - Lydia M Contreras
- McKetta Department of Chemical Engineering, University of Texas at Austin, 200 E. Dean Keeton St., Stop C0400, Austin, TX 78712, USA
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31
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Amini ZN, Olson KE, Müller UF. Spliceozymes: ribozymes that remove introns from pre-mRNAs in trans. PLoS One 2014; 9:e101932. [PMID: 25014025 PMCID: PMC4094466 DOI: 10.1371/journal.pone.0101932] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2013] [Accepted: 06/13/2014] [Indexed: 11/25/2022] Open
Abstract
Group I introns are pre-mRNA introns that do not require the spliceosome for their removal. Instead, they fold into complex three-dimensional structures and catalyze two transesterification reactions, thereby excising themselves and joining the flanking exons. These catalytic RNAs (ribozymes) have been modified previously to work in trans, whereby the ribozymes can recognize a splice site on a substrate RNA and replace the 5′- or 3′-portion of the substrate. Here we describe a new variant of the group I intron ribozyme from Tetrahymena that recognizes two splice sites on a substrate RNA, removes the intron sequences between the splice sites, and joins the flanking exons, analogous to the action of the spliceosome. This ‘group I spliceozyme’ functions in vitro and in vivo, and it is able to mediate a growth phenotype in E. coli cells. The intron sequences of the target pre-mRNAs are constrained near the splice sites but can carry a wide range of sequences in their interior. Because the splice site recognition sequences can be adjusted to different splice sites, the spliceozyme may have the potential for wide applications as tool in research and therapy.
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Affiliation(s)
- Zhaleh N. Amini
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, United States of America
| | - Karen E. Olson
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, United States of America
| | - Ulrich F. Müller
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, United States of America
- * E-mail:
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32
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Hausner G, Hafez M, Edgell DR. Bacterial group I introns: mobile RNA catalysts. Mob DNA 2014; 5:8. [PMID: 24612670 PMCID: PMC3984707 DOI: 10.1186/1759-8753-5-8] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Accepted: 02/24/2014] [Indexed: 12/02/2022] Open
Abstract
Group I introns are intervening sequences that have invaded tRNA, rRNA and protein coding genes in bacteria and their phages. The ability of group I introns to self-splice from their host transcripts, by acting as ribozymes, potentially renders their insertion into genes phenotypically neutral. Some group I introns are mobile genetic elements due to encoded homing endonuclease genes that function in DNA-based mobility pathways to promote spread to intronless alleles. Group I introns have a limited distribution among bacteria and the current assumption is that they are benign selfish elements, although some introns and homing endonucleases are a source of genetic novelty as they have been co-opted by host genomes to provide regulatory functions. Questions regarding the origin and maintenance of group I introns among the bacteria and phages are also addressed.
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Affiliation(s)
- Georg Hausner
- Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2 N2, Canada
| | - Mohamed Hafez
- Department of Biochemistry, Faculty of Medicine, University of Montreal, Montréal, QC H3C 3 J7, Canada
- Department of Botany, Faculty of Science, Suez University, Suez, Egypt
| | - David R Edgell
- Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, London, ON N6A 5C1, Canada
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33
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Olson KE, Dolan GF, Müller UF. In vivo evolution of a catalytic RNA couples trans-splicing to translation. PLoS One 2014; 9:e86473. [PMID: 24466112 PMCID: PMC3900562 DOI: 10.1371/journal.pone.0086473] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2013] [Accepted: 12/09/2013] [Indexed: 12/17/2022] Open
Abstract
How does a non-coding RNA evolve in cells? To address this question experimentally we evolved a trans-splicing variant of the group I intron ribozyme from Tetrahymena over 21 cycles of evolution in E.coli cells. Sequence variation was introduced during the evolution by mutagenic and recombinative PCR, and increasingly active ribozymes were selected by their repair of an mRNA mediating antibiotic resistance. The most efficient ribozyme contained four clustered mutations that were necessary and sufficient for maximum activity in cells. Surprisingly, these mutations did not increase the trans-splicing activity of the ribozyme. Instead, they appear to have recruited a cellular protein, the transcription termination factor Rho, and facilitated more efficient translation of the ribozyme’s trans-splicing product. In addition, these mutations affected the expression of several other, unrelated genes. These results suggest that during RNA evolution in cells, four mutations can be sufficient to evolve new protein interactions, and four mutations in an RNA molecule can generate a large effect on gene regulation in the cell.
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Affiliation(s)
- Karen E. Olson
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, United States of America
| | - Gregory F. Dolan
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, United States of America
| | - Ulrich F. Müller
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, United States of America
- * E-mail:
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34
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Nyati S, Bhattacharya D, Werth S, Honegger R. Phylogenetic analysis of LSU and SSU rDNA group I introns of lichen photobionts associated with the genera Xanthoria and Xanthomendoza (Teloschistaceae, lichenized Ascomycetes). JOURNAL OF PHYCOLOGY 2013; 49:10.1111/jpy.12126. [PMID: 24415800 PMCID: PMC3885279 DOI: 10.1111/jpy.12126] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
We studied group I introns in sterile cultures of selected groups of lichen photobionts, focusing on Trebouxia species associated with Xanthoria s. lat. (including Xanthomendoza spp.; lichen-forming ascomycetes). Group I introns were found inserted after position 798 (Escherichia coli numbering) in the large subunit (LSU) rRNA in representatives of the green algal genera Trebouxia and Asterochloris. The 798 intron was found in about 25% of Xanthoria photobionts including several reference strains obtained from algal culture collections. An alignment of LSU-encoded rDNA intron sequences revealed high similarity of these sequences allowing their phylogenetic analysis. The 798 group I intron phylogeny was largely congruent with a phylogeny of the Internal Transcribed Spacer Region (ITS), indicating that the insertion of the intron most likely occurred in the common ancestor of the genera Trebouxia and Asterochloris. The intron was vertically inherited in some taxa, but lost in others. The high sequence similarity of this intron to one found in Chlorella angustoellipsoidea suggests that the 798 intron was either present in the common ancestor of Trebouxiophyceae, or that its present distribution results from more recent horizontal transfers, followed by vertical inheritance and loss. Analysis of another group I intron shared by these photobionts at small subunit (SSU) position 1512 supports the hypothesis of repeated lateral transfers of this intron among some taxa, but loss among others. Our data confirm that the history of group I introns is characterized by repeated horizontal transfers, and suggests that some of these introns have ancient origins within Chlorophyta.
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Affiliation(s)
- Shyam Nyati
- Author for correspondence: phone: +1 734 763 0921 fax: +1 734 763 5447
| | - Debashish Bhattacharya
- Department of Ecology, Evolution and Natural Resources and Institute of Marine and Coastal Science, Rutgers University, 59 Dudley Road, New Brunswick, New Jersey 08901, USA
| | - Silke Werth
- Faculty of Life- and Environmental Sciences, University of Iceland, Sturlugata 7, 101 Reykjavík, Iceland
| | - Rosmarie Honegger
- Institute of Plant Biology, University of Zurich, Zollikerstrasse 107, 8008 Zurich, Switzerland
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35
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Papaioannou IA, Dimopoulou CD, Typas MA. "Cryptic" group-I introns in the nuclear SSU-rRNA gene of Verticillium dahliae. Curr Genet 2013; 60:135-48. [PMID: 24258678 DOI: 10.1007/s00294-013-0417-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2013] [Revised: 10/24/2013] [Accepted: 11/06/2013] [Indexed: 11/30/2022]
Abstract
Group-I introns are widespread--though irregularly distributed--in eukaryotic organisms, and they have been extensively used for discrimination and phylogenetic analyses. Within the Verticillium genus, which comprises important phytopathogenic fungi, a group-I intron was previously identified in the SSU-rRNA (18S) gene of only V. longisporum. In this work, we aimed at elucidating the SSU-located intron distribution in V. dahliae and other Verticillium species, and the assessment of heterogeneity regarding intron content among rDNA repeats of fungal strains. Using conserved PCR primers for the amplification of the SSU gene, a structurally similar novel intron (sub-group IC1) was detected in only a few V. dahliae isolates. However, when intron-specific primers were used for the screening of a diverse collection of Verticillium isolates that originally failed to produce intron-containing SSU amplicons, most were found to contain one or both intron types, at variable rDNA repeat numbers. This marked heterogeneity was confirmed with qRT-PCR by testing rDNA copy numbers (varying from 39 to 70 copies per haploid genome) and intron copy ratios in selected isolates. Our results demonstrate that (a) IC1 group-I introns are not specific to V. longisporum within the Verticillium genus, (b) V. dahliae isolates of vegetative compatibility groups (VCGs) 4A and 6, which bear the novel intron at most of their rDNA repeats, are closely related, and (c) there is considerable intra-genomic heterogeneity for the presence or absence of introns among the ribosomal repeats. These findings underline that distributions of introns in the highly heterogeneous repetitive rDNA complex should always be verified with sensitive methods to avoid misleading conclusions for the phylogeny of fungi and other organisms.
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Affiliation(s)
- Ioannis A Papaioannou
- Department of Genetics and Biotechnology, Faculty of Biology, National and Kapodistrian University of Athens, Panepistimiopolis, 15701, Athens, Greece
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36
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Evolutionary dynamics of introns and their open reading frames in the U7 region of the mitochondrial rnl gene in species of Ceratocystis. Fungal Biol 2013; 117:791-806. [DOI: 10.1016/j.funbio.2013.10.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2013] [Revised: 10/12/2013] [Accepted: 10/14/2013] [Indexed: 12/31/2022]
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37
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Xu C, Wang C, Sun X, Zhang R, Gleason ML, Eiji T, Sun G. Multiple group I introns in the small-subunit rDNA of Botryosphaeria dothidea: implication for intraspecific genetic diversity. PLoS One 2013; 8:e67808. [PMID: 23844098 PMCID: PMC3699495 DOI: 10.1371/journal.pone.0067808] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2013] [Accepted: 05/22/2013] [Indexed: 11/18/2022] Open
Abstract
Botryosphaeria dothidea is a widespread and economically important pathogen on various fruit trees, and it often causes die-back and canker on limbs and fruit rot. In characterizing intraspecies genetic variation within this fungus, group I introns, rich in rDNA of fungi, may provide a productive region for exploration. In this research, we analysed complete small subunit (SSU) ribosomal DNA (rDNA) sequences of 37 B. dothidea strains, and found four insertions, designated Bdo.S943, Bdo.S1199-A, Bdo.S1199-B and Bdo.S1506, at three positions. Sequence analysis and structure prediction revealed that both Bdo.S943 and Bdo.S1506 belonged to subgroup IC1 of group I introns, whereas Bdo.S1199-A and Bdo.S1199-B corresponded to group IE introns. Moreover, Bdo.S1199-A was found to host an open reading frame (ORF) for encoding the homing endonuclease (HE), whereas Bdo.S1199-B, an evolutionary descendant of Bdo.S1199-A, included a degenerate HE. The above four introns were novel, and were the first group I introns observed and characterized in this species. Differential distribution of these introns revealed that all strains could be separated into four genotypes. Genotype III (no intron) and genotype IV (Bdo.S1199-B) were each found in only one strain, whereas genotype I (Bdo.S1199-A) and genotype II (Bdo.S943 and Bdo.S1506) occurred in 95% of the strains. There is a correlation between B. dothidea genotypes and hosts or geographic locations. Thus, these newly discovered group I introns can help to advance understanding of genetic differentiation within B. dothidea.
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Affiliation(s)
- Chao Xu
- Key Laboratory of Crop Stress Biology in Arid Areas, College of Plant Protection, Northwest A&F University, Yangling, Shaanxi, China
| | - Chunsheng Wang
- Key Laboratory of Crop Stress Biology in Arid Areas, College of Plant Protection, Northwest A&F University, Yangling, Shaanxi, China
| | - Xinyao Sun
- Key Laboratory of Crop Stress Biology in Arid Areas, College of Plant Protection, Northwest A&F University, Yangling, Shaanxi, China
| | - Rong Zhang
- Key Laboratory of Crop Stress Biology in Arid Areas, College of Plant Protection, Northwest A&F University, Yangling, Shaanxi, China
| | - Mark L. Gleason
- Department of Plant Pathology and Microbiology, Iowa State University, Ames, Iowa, United States of America
| | - Tanaka Eiji
- Ishikawa Prefectural University, Ishikawa, Japan
| | - Guangyu Sun
- Key Laboratory of Crop Stress Biology in Arid Areas, College of Plant Protection, Northwest A&F University, Yangling, Shaanxi, China
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38
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González D. Identification, molecular characterization, and evolution of group I introns at the expansion segment D11 of 28S rDNA in Rhizoctonia species. Fungal Biol 2013; 117:623-37. [PMID: 24012302 DOI: 10.1016/j.funbio.2013.06.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2012] [Revised: 06/03/2013] [Accepted: 06/19/2013] [Indexed: 10/26/2022]
Abstract
The nuclear ribosomal DNA of Rhizoctonia species is polymorphic in terms of the nucleotide composition and length. Insertions of 349-410 nucleotides in length with characteristics of group I introns were detected at a single insertion point at the expansion segment D11 of 28S rDNA in 12 out of 64 isolates. Eleven corresponded to Rhizoctonia solani (teleomorph: Thanatephorous) and one (AG-Q) to Rhizoctonia spp. (teleomorph: Ceratobasidium). Sequence data showed that all but AG-Q contained conserved DNA catalytic core regions (P, Q, R, and S) essential for selfsplicing. The predicted secondary structure revealed that base-paired helices corresponded to subgroup IC1. Isolates from same anastomosis group and even subgroups within R. solani were variable with regard to possession of introns. Phylogenetic analyses indicated that introns were vertically transmitted. Unfortunately, sequence data from the conserved region from all 64 isolates were not useful for delimiting species. Analyses with IC1 introns at same insertion point, of both Ascomycota and Basidiomycota indicated the possibility of horizontal transfer at this site. The present study uncovered new questions on evolutionary pattern of change of these introns within Rhizoctonia species.
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Affiliation(s)
- Dolores González
- Instituto de Ecología, A.C., Red de Biodiversidad y Sistemática, Carretera Antigua a Coatepec No. 351, El Haya, Xalapa 91070, Veracruz, Mexico.
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39
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The mtDNA rns gene landscape in the Ophiostomatales and other fungal taxa: Twintrons, introns, and intron-encoded proteins. Fungal Genet Biol 2013; 53:71-83. [DOI: 10.1016/j.fgb.2013.01.005] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2012] [Revised: 01/06/2013] [Accepted: 01/15/2013] [Indexed: 12/17/2022]
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40
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Manzourolajdad A, Wang Y, Shaw TI, Malmberg RL. Information-theoretic uncertainty of SCFG-modeled folding space of the non-coding RNA. J Theor Biol 2012; 318:140-63. [PMID: 23160142 DOI: 10.1016/j.jtbi.2012.10.023] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Revised: 10/11/2012] [Accepted: 10/18/2012] [Indexed: 10/27/2022]
Abstract
UNLABELLED RNA secondary structure ensembles define probability distributions for alternative equilibrium secondary structures of an RNA sequence. Shannon's entropy is a measure for the amount of diversity present in any ensemble. In this work, Shannon's entropy of the SCFG ensemble on an RNA sequence is derived and implemented in polynomial time for both structurally ambiguous and unambiguous grammars. Micro RNA sequences generally have low folding entropy, as previously discovered. Surprisingly, signs of significantly high folding entropy were observed in certain ncRNA families. More effective models coupled with targeted randomization tests can lead to a better insight into folding features of these families. AVAILABILITY URL http://www.plantbio.uga.edu/~russell/index.php?s=1&n=5&r=0.
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Affiliation(s)
- Amirhossein Manzourolajdad
- Institute of Bioinformatics, University of Georgia, Davison Life Sciences Bldg, Room B118B, 120 Green St, Athens, GA 30602, USA.
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41
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Rudski SM, Hausner G. The mtDNA rps3 locus has been invaded by a group I intron in some species of Grosmannia. MYCOSCIENCE 2012. [DOI: 10.1007/s10267-012-0183-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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42
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Fedrowitz K, Kaasalainen U, Rikkinen J. Geographic mosaic of symbiont selectivity in a genus of epiphytic cyanolichens. Ecol Evol 2012; 2:2291-303. [PMID: 23139887 PMCID: PMC3488679 DOI: 10.1002/ece3.343] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2012] [Revised: 07/03/2012] [Accepted: 07/04/2012] [Indexed: 11/26/2022] Open
Abstract
In symbiotic systems, patterns of symbiont diversity and selectivity are crucial for the understanding of fundamental ecological processes such as dispersal and establishment. The lichen genus Nephroma (Peltigerales, Ascomycota) has a nearly cosmopolitan distribution and is thus an attractive model for the study of symbiotic interactions over a wide range of spatial scales. In this study, we analyze the genetic diversity of Nephroma mycobionts and their associated Nostoc photobionts within a global framework. The study is based on Internal Transcribed Spacer (ITS) sequences of fungal symbionts and tRNA(L) (eu) (UAA) intron sequences of cyanobacterial symbionts. The full data set includes 271 Nephroma and 358 Nostoc sequences, with over 150 sequence pairs known to originate from the same lichen thalli. Our results show that all bipartite Nephroma species associate with one group of Nostoc different from Nostoc typically found in tripartite Nephroma species. This conserved association appears to have been inherited from the common ancestor of all extant species. While specific associations between some symbiont genotypes can be observed over vast distances, both symbionts tend to show genetic differentiation over wide geographic scales. Most bipartite Nephroma species share their Nostoc symbionts with one or more other fungal taxa, and no fungal species associates solely with a single Nostoc genotype, supporting the concept of functional lichen guilds. Symbiont selectivity patterns within these lichens are best described as a geographic mosaic, with higher selectivity locally than globally. This may reflect specific habitat preferences of particular symbiont combinations, but also the influence of founder effects.
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Affiliation(s)
- Katja Fedrowitz
- Department of Ecology, Swedish University of Agricultural Sciences (SLU) P.O. 7044, SE-750 07, Uppsala, Sweden
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I-PfoP3I: a novel nicking HNH homing endonuclease encoded in the group I intron of the DNA polymerase gene in Phormidium foveolarum phage Pf-WMP3. PLoS One 2012; 7:e43738. [PMID: 22952751 PMCID: PMC3428280 DOI: 10.1371/journal.pone.0043738] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2012] [Accepted: 07/27/2012] [Indexed: 11/19/2022] Open
Abstract
Homing endonucleases encoded in a group I self-splicing intron in a protein-coding gene in cyanophage genomes have not been reported, apart from some free-standing homing edonucleases. In this study, a nicking DNA endonuclease, I-PfoP3I, encoded in a group IA2 intron in the DNA polymerase gene of a T7-like cyanophage Pf-WMP3, which infects the freshwater cyanobacterium Phormidium foveolarum is described. The Pf-WMP3 intron splices efficiently in vivo and self-splices in vitro simultaneously during transcription. I-PfoP3I belongs to the HNH family with an unconventional C-terminal HNH motif. I-PfoP3I nicks the intron-minus Pf-WMP3 DNA polymerase gene more efficiently than the Pf-WMP4 DNA polymerase gene that lacks any intervening sequence in vitro, indicating the variable capacity of I-PfoP3I. I-PfoP3I cleaves 4 nt upstream of the intron insertion site on the coding strand of EXON 1 on both intron-minus Pf-WMP3 and Pf-WMP4 DNA polymerase genes. Using an in vitro cleavage assay and scanning deletion mutants of the intronless target site, the minimal recognition site was determined to be a 14 bp region downstream of the cut site. I-PfoP3I requires Mg2+, Ca2+ or Mn2+ for nicking activity. Phylogenetic analysis suggests that the intron and homing endonuclease gene elements might be inserted in Pf-WMP3 genome individually after differentiation from Pf-WMP4. To our knowledge, this is the first report of the presence of a group I self-splicing intron encoding a functional homing endonuclease in a protein-coding gene in a cyanophage genome.
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Meluzzi D, Olson KE, Dolan GF, Arya G, Müller UF. Computational prediction of efficient splice sites for trans-splicing ribozymes. RNA (NEW YORK, N.Y.) 2012; 18:590-602. [PMID: 22274956 PMCID: PMC3285945 DOI: 10.1261/rna.029884.111] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2011] [Accepted: 12/02/2011] [Indexed: 05/31/2023]
Abstract
Group I introns have been engineered into trans-splicing ribozymes capable of replacing the 3'-terminal portion of an external mRNA with their own 3'-exon. Although this design makes trans-splicing ribozymes potentially useful for therapeutic application, their trans-splicing efficiency is usually too low for medical use. One factor that strongly influences trans-splicing efficiency is the position of the target splice site on the mRNA substrate. Viable splice sites are currently determined using a biochemical trans-tagging assay. Here, we propose a rapid and inexpensive alternative approach to identify efficient splice sites. This approach involves the computation of the binding free energies between ribozyme and mRNA substrate. We found that the computed binding free energies correlate well with the trans-splicing efficiency experimentally determined at 18 different splice sites on the mRNA of chloramphenicol acetyl transferase. In contrast, our results from the trans-tagging assay correlate less well with measured trans-splicing efficiency. The computed free energy components suggest that splice site efficiency depends on the following secondary structure rearrangements: hybridization of the ribozyme's internal guide sequence (IGS) with mRNA substrate (most important), unfolding of substrate proximal to the splice site, and release of the IGS from the 3'-exon (least important). The proposed computational approach can also be extended to fulfill additional design requirements of efficient trans-splicing ribozymes, such as the optimization of 3'-exon and extended guide sequences.
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Affiliation(s)
- Dario Meluzzi
- Department of Chemistry and Biochemistry, University of California, San Diego, California 92093, USA
- Department of NanoEngineering, University of California, San Diego, California 92093, USA
| | - Karen E. Olson
- Department of Chemistry and Biochemistry, University of California, San Diego, California 92093, USA
| | - Gregory F. Dolan
- Department of Chemistry and Biochemistry, University of California, San Diego, California 92093, USA
| | - Gaurav Arya
- Department of NanoEngineering, University of California, San Diego, California 92093, USA
| | - Ulrich F. Müller
- Department of Chemistry and Biochemistry, University of California, San Diego, California 92093, USA
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Heid CG, Ottiger P, Leist R, Leutwyler S. The S1/S2 exciton interaction in 2-pyridone·6-methyl-2-pyridone: Davydov splitting, vibronic coupling, and vibronic quenching. J Chem Phys 2012; 135:154311. [PMID: 22029317 DOI: 10.1063/1.3652759] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The excitonic splitting between the S(1) and S(2) electronic states of the doubly hydrogen-bonded dimer 2-pyridone[middle dot]6-methyl-2-pyridone (2PY·6M2PY) is studied in a supersonic jet, applying two-color resonant two-photon ionization (2C-R2PI), UV-UV depletion, and dispersed fluorescence spectroscopies. In contrast to the C(2h) symmetric (2-pyridone)(2) homodimer, in which the S(1) ← S(0) transition is symmetry-forbidden but the S(2) ← S(0) transition is allowed, the symmetry-breaking by the additional methyl group in 2PY·6M2PY leads to the appearance of both the S(1) and S(2) origins, which are separated by Δ(exp) = 154 cm(-1). When combined with the separation of the S(1) ← S(0) excitations of 6M2PY and 2PY, which is δ = 102 cm(-1), one obtains an S(1)/S(2) exciton coupling matrix element of V(AB, el) = 57 cm(-1) in a Frenkel-Davydov exciton model. The vibronic couplings in the S(1)/S(2) ← S(0) spectrum of 2PY·6M2PY are treated by the Fulton-Gouterman single-mode model. We consider independent couplings to the intramolecular 6a(') vibration and to the intermolecular σ(') stretch, and obtain a semi-quantitative fit to the observed spectrum. The dimensionless excitonic couplings are C(6a(')) = 0.15 and C(σ(')) = 0.05, which places this dimer in the weak-coupling limit. However, the S(1)/S(2) state exciton splittings Δ(calc) calculated by the configuration interaction singles method (CIS), time-dependent Hartree-Fock (TD-HF), and approximate second-order coupled-cluster method (CC2) are between 1100 and 1450 cm(-1), or seven to nine times larger than observed. These huge errors result from the neglect of the coupling to the optically active intra- and intermolecular vibrations of the dimer, which lead to vibronic quenching of the purely electronic excitonic splitting. For 2PY·6M2PY the electronic splitting is quenched by a factor of ~30 (i.e., the vibronic quenching factor is Γ(exp) = 0.035), which brings the calculated splittings into close agreement with the experimentally observed value. The 2C-R2PI and fluorescence spectra of the tautomeric species 2-hydroxypyridine·6-methyl-2-pyridone (2HP·6M2PY) are also observed and assigned.
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Affiliation(s)
- Cornelia G Heid
- Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3000 Bern 9, Switzerland
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Kladwang W, Chou FC, Das R. Automated RNA structure prediction uncovers a kink-turn linker in double glycine riboswitches. J Am Chem Soc 2012; 134:1404-7. [PMID: 22192063 DOI: 10.1021/ja2093508] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The tertiary structures of functional RNA molecules remain difficult to decipher. A new generation of automated RNA structure prediction methods may help address these challenges but have not yet been experimentally validated. Here we apply four prediction tools to a class of double glycine riboswitches that can bind two ligands cooperatively. A novel method (BPPalign), RMdetect, JAR3D, and Rosetta 3D modeling give consistent predictions for a new stem P0 and a kink-turn motif. These elements structure the linker between the RNAs' double aptamers. Chemical mapping on the Fusobacterium nucleatum riboswitch with N-methylisatoic anhydride, dimethyl sulfate and 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimide metho-p-toluenesulfonate probing, mutate-and-map studies, and mutation/rescue experiments all provide strong evidence for the structured linker. Under solution conditions that permit rigorous thermodynamic analysis, disrupting this helix-junction-helix structure gives 120- and 6-30-fold poorer dissociation constants for the RNA's two glycine-binding transitions, corresponding to an overall energetic impact of 4.3 ± 0.5 kcal/mol. Prior biochemical and crystallography studies did not include this critical element due to over-truncation of the RNA. We speculate that several further undiscovered elements are likely to exist in the flanking regions of this and other functional RNAs, and automated prediction tools can play a useful role in their detection and dissection.
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Affiliation(s)
- Wipapat Kladwang
- Department of Biochemistry, Stanford University, Stanford, California 94305, USA
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Hafez M, Iranpour M, Mullineux ST, Sethuraman J, Wosnitza KM, Lehn P, Kroeker J, Loewen PC, Reid J, Hausner G. Identification of group I introns within the SSU rDNA gene in species of Ceratocystiopsis and related taxa. Fungal Biol 2012; 116:98-111. [DOI: 10.1016/j.funbio.2011.10.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Revised: 10/17/2011] [Accepted: 10/18/2011] [Indexed: 11/28/2022]
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Shareghi P, Wang Y, Malmberg R, Cai L. Simultaneous prediction of RNA secondary structure and helix coaxial stacking. BMC Genomics 2012; 13 Suppl 3:S7. [PMID: 22759616 PMCID: PMC3394421 DOI: 10.1186/1471-2164-13-s3-s7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Background RNA secondary structure plays a scaffolding role for RNA tertiary conformation. Accurate secondary structure prediction can not only identify double-stranded helices and single stranded-loops but also help provide information for potential tertiary interaction motifs critical to the 3D conformation. The average accuracy in ab initio prediction remains 70%; performance improvement has only been limited to short RNA sequences. The prediction of tertiary interaction motifs is difficult without multiple, related sequences that are usually not available. This paper presents research that aims to improve the secondary structure prediction performance and to develop a capability to predict coaxial stacking between helices. Coaxial stacking positions two helices on the same axis, a tertiary motif present in almost all junctions that account for a high percentage of RNA tertiary structures. Results This research identified energetic rules for coaxial stacks and geometric constraints on stack combinations, which were applied to developing an efficient dynamic programming application for simultaneous prediction of secondary structure and coaxial stacking. Results on a number of non-coding RNA data sets, of short and moderately long lengths, show a performance improvement (specially on tRNAs) for secondary structure prediction when compared with existing methods. The program also demonstrates a capability for prediction of coaxial stacking. Conclusions The significant leap of performance on tRNAs demonstrated in this work suggests that a breakthrough to a higher performance in RNA secondary structure prediction may lie in understanding contributions from tertiary motifs critical to the structure, as such information can be used to constrain geometrically as well as energetically the space of RNA secondary structure.
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Brown MW, Silberman JD, Spiegel FW. A contemporary evaluation of the acrasids (Acrasidae, Heterolobosea, Excavata). Eur J Protistol 2011; 48:103-23. [PMID: 22154141 DOI: 10.1016/j.ejop.2011.10.001] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2011] [Revised: 10/18/2011] [Accepted: 10/19/2011] [Indexed: 11/29/2022]
Abstract
Sorocarpic protists are organisms that individually aggregate and work together to form a fungus-like fruiting body (sorocarp). The amoeboid forms are often colloquially referred to as "cellular slime molds" or "acrasids". We argue the latter term should be used only to refer to members of Acrasidae in Heterolobosea. Here we study the diversity of two Acrasidae genera, Acrasis and the closely similar Pocheina, using a combination of morphological characteristics and small subunit rRNA gene sequences. A total of eight isolates of Acrasis and an example of Pocheina were examined. Acrasis/Pocheina form a well-supported monophyletic group that is the highly supported sister to a clade containing Allovahlkampfia and several other amoebae. Four molecular lineages of Acrasis were resolved, each of which is characterized by a distinctive fruiting body morphology. Each lineage represents a species, two of which are novel, Acrasis kona n. sp. and Acrasis takarsan n. sp. An isolate identified as Pocheina rosea is nested within the clade containing isolates of the taxon Acrasis rosea, into which P. rosea is tentatively subsumed. One member of the tightly knit allovahlkampfid clade was induced to form a simple sorocarp, leading us to include this clade in Acrasidae.
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Affiliation(s)
- Matthew W Brown
- Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701, USA.
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Kikovska E, Wu S, Mao G, Kirsebom LA. Cleavage mediated by the P15 domain of bacterial RNase P RNA. Nucleic Acids Res 2011; 40:2224-33. [PMID: 22102593 PMCID: PMC3299987 DOI: 10.1093/nar/gkr1001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Independently folded domains in RNAs frequently adopt identical tertiary structures regardless of whether they are in isolation or are part of larger RNA molecules. This is exemplified by the P15 domain in the RNA subunit (RPR) of the universally conserved endoribonuclease P, which is involved in the processing of tRNA precursors. One of its domains, encompassing the P15 loop, binds to the 3'-end of tRNA precursors resulting in the formation of the RCCA-RNase P RNA interaction (interacting residues underlined) in the bacterial RPR-substrate complex. The function of this interaction was hypothesized to anchor the substrate, expose the cleavage site and result in re-coordination of Mg(2+) at the cleavage site. Here we show that small model-RNA molecules (~30 nt) carrying the P15-loop mediated cleavage at the canonical RNase P cleavage site with significantly reduced rates compared to cleavage with full-size RPR. These data provide further experimental evidence for our model that the P15 domain contributes to both substrate binding and catalysis. Our data raises intriguing evolutionary possibilities for 'RNA-mediated' cleavage of RNA.
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Affiliation(s)
- Ema Kikovska
- Department of Cell and Molecular Biology, Box 596, Biomedical Centre, SE-751 24 Uppsala, Sweden
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