1
|
Romero Romero ML, Landerer C, Poehls J, Toth‐Petroczy A. Phenotypic mutations contribute to protein diversity and shape protein evolution. Protein Sci 2022; 31:e4397. [PMID: 36040266 PMCID: PMC9375231 DOI: 10.1002/pro.4397] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Revised: 06/14/2022] [Accepted: 07/04/2022] [Indexed: 11/16/2022]
Abstract
Errors in DNA replication generate genetic mutations, while errors in transcription and translation lead to phenotypic mutations. Phenotypic mutations are orders of magnitude more frequent than genetic ones, yet they are less understood. Here, we review the types of phenotypic mutations, their quantifications, and their role in protein evolution and disease. The diversity generated by phenotypic mutation can facilitate adaptive evolution. Indeed, phenotypic mutations, such as ribosomal frameshift and stop codon readthrough, sometimes serve to regulate protein expression and function. Phenotypic mutations have often been linked to fitness decrease and diseases. Thus, understanding the protein heterogeneity and phenotypic diversity caused by phenotypic mutations will advance our understanding of protein evolution and have implications on human health and diseases.
Collapse
Affiliation(s)
- Maria Luisa Romero Romero
- Max Planck Institute of Molecular Cell Biology and GeneticsDresdenGermany
- Center for Systems Biology DresdenDresdenGermany
| | - Cedric Landerer
- Max Planck Institute of Molecular Cell Biology and GeneticsDresdenGermany
- Center for Systems Biology DresdenDresdenGermany
| | - Jonas Poehls
- Max Planck Institute of Molecular Cell Biology and GeneticsDresdenGermany
- Center for Systems Biology DresdenDresdenGermany
| | - Agnes Toth‐Petroczy
- Max Planck Institute of Molecular Cell Biology and GeneticsDresdenGermany
- Center for Systems Biology DresdenDresdenGermany
- Cluster of Excellence Physics of LifeTU DresdenDresdenGermany
| |
Collapse
|
2
|
Malinova I, Zupok A, Massouh A, Schöttler MA, Meyer EH, Yaneva-Roder L, Szymanski W, Rößner M, Ruf S, Bock R, Greiner S. Correction of frameshift mutations in the atpB gene by translational recoding in chloroplasts of Oenothera and tobacco. THE PLANT CELL 2021; 33:1682-1705. [PMID: 33561268 PMCID: PMC8254509 DOI: 10.1093/plcell/koab050] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Accepted: 02/02/2021] [Indexed: 05/10/2023]
Abstract
Translational recoding, also known as ribosomal frameshifting, is a process that causes ribosome slippage along the messenger RNA, thereby changing the amino acid sequence of the synthesized protein. Whether the chloroplast employs recoding is unknown. I-iota, a plastome mutant of Oenothera (evening primrose), carries a single adenine insertion in an oligoA stretch [11A] of the atpB coding region (encoding the β-subunit of the ATP synthase). The mutation is expected to cause synthesis of a truncated, nonfunctional protein. We report that a full-length AtpB protein is detectable in I-iota leaves, suggesting operation of a recoding mechanism. To characterize the phenomenon, we generated transplastomic tobacco lines in which the atpB reading frame was altered by insertions or deletions in the oligoA motif. We observed that insertion of two adenines was more efficiently corrected than insertion of a single adenine, or deletion of one or two adenines. We further show that homopolymeric composition of the oligoA stretch is essential for recoding, as an additional replacement of AAA lysine codon by AAG resulted in an albino phenotype. Our work provides evidence for the operation of translational recoding in chloroplasts. Recoding enables correction of frameshift mutations and can restore photoautotrophic growth in the presence of a mutation that otherwise would be lethal.
Collapse
Affiliation(s)
- Irina Malinova
- Department Organelle Biology, Biotechnology and Molecular Ecophysiology, Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| | - Arkadiusz Zupok
- Department Organelle Biology, Biotechnology and Molecular Ecophysiology, Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| | - Amid Massouh
- Department Organelle Biology, Biotechnology and Molecular Ecophysiology, Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| | - Mark Aurel Schöttler
- Department Organelle Biology, Biotechnology and Molecular Ecophysiology, Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| | - Etienne H Meyer
- Department Organelle Biology, Biotechnology and Molecular Ecophysiology, Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| | - Liliya Yaneva-Roder
- Department Organelle Biology, Biotechnology and Molecular Ecophysiology, Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| | - Witold Szymanski
- Department Organelle Biology, Biotechnology and Molecular Ecophysiology, Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| | - Margit Rößner
- Department Organelle Biology, Biotechnology and Molecular Ecophysiology, Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| | - Stephanie Ruf
- Department Organelle Biology, Biotechnology and Molecular Ecophysiology, Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| | - Ralph Bock
- Department Organelle Biology, Biotechnology and Molecular Ecophysiology, Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| | - Stephan Greiner
- Department Organelle Biology, Biotechnology and Molecular Ecophysiology, Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| |
Collapse
|
3
|
Detection and Characterization of Diphtheria Toxin Gene-Bearing Corynebacterium Species through a New Real-Time PCR Assay. J Clin Microbiol 2020; 58:JCM.00639-20. [PMID: 32727830 DOI: 10.1128/jcm.00639-20] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2020] [Accepted: 07/26/2020] [Indexed: 11/20/2022] Open
Abstract
Respiratory diphtheria, characterized by a firmly adherent pseudomembrane, is caused by toxin-producing strains of Corynebacterium diphtheriae, with similar illness produced occasionally by toxigenic Corynebacterium ulcerans or, rarely, Corynebacterium pseudotuberculosis While diphtheria laboratory confirmation requires culture methods to determine toxigenicity, real-time PCR (RT-PCR) provides a faster method to detect the toxin gene (tox). Nontoxigenic tox-bearing (NTTB) Corynebacterium isolates have been described, but impact of these isolates on the accuracy of molecular diagnostics is not well characterized. Here, we describe a new triplex RT-PCR assay to detect tox and distinguish C. diphtheriae from the closely related species C. ulcerans and C. pseudotuberculosis Analytical sensitivity and specificity of the assay were assessed in comparison to culture using 690 previously characterized microbial isolates. The new triplex assay characterized Corynebacterium isolates accurately, with 100% analytical sensitivity for all targets. Analytical specificity with isolates was 94.1%, 100%, and 99.5% for tox, Diph_rpoB, and CUP_rpoB targets, respectively. Twenty-nine NTTB Corynebacterium isolates, representing 5.9% of 494 nontoxigenic isolates tested, were detected by RT-PCR. Whole-genome sequencing of NTTB isolates revealed varied mutations putatively underlying their lack of toxin production, as well as eight isolates with no mutation in tox or the promoter region. This new Corynebacterium RT-PCR method provides a rapid tool to screen isolates and identify probable diphtheria cases directly from specimens. However, the sporadic occurrence of NTTB isolates reinforces the viewpoint that diphtheria culture diagnostics continue to provide the most accurate case confirmation.
Collapse
|
4
|
Gunderson EL, Vogel I, Chappell L, Bulman CA, Lim KC, Luo M, Whitman JD, Franklin C, Choi YJ, Lefoulon E, Clark T, Beerntsen B, Slatko B, Mitreva M, Sullivan W, Sakanari JA. The endosymbiont Wolbachia rebounds following antibiotic treatment. PLoS Pathog 2020; 16:e1008623. [PMID: 32639986 PMCID: PMC7371230 DOI: 10.1371/journal.ppat.1008623] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 07/20/2020] [Accepted: 05/13/2020] [Indexed: 12/20/2022] Open
Abstract
Antibiotic treatment has emerged as a promising strategy to sterilize and kill filarial nematodes due to their dependence on their endosymbiotic bacteria, Wolbachia. Several studies have shown that novel and FDA-approved antibiotics are efficacious at depleting the filarial nematodes of their endosymbiont, thus reducing female fecundity. However, it remains unclear if antibiotics can permanently deplete Wolbachia and cause sterility for the lifespan of the adult worms. Concerns about resistance arising from mass drug administration necessitate a careful exploration of potential Wolbachia recrudescence. In the present study, we investigated the long-term effects of the FDA-approved antibiotic, rifampicin, in the Brugia pahangi jird model of infection. Initially, rifampicin treatment depleted Wolbachia in adult worms and simultaneously impaired female worm fecundity. However, during an 8-month washout period, Wolbachia titers rebounded and embryogenesis returned to normal. Genome sequence analyses of Wolbachia revealed that despite the population bottleneck and recovery, no genetic changes occurred that could account for the rebound. Clusters of densely packed Wolbachia within the worm's ovarian tissues were observed by confocal microscopy and remained in worms treated with rifampicin, suggesting that they may serve as privileged sites that allow Wolbachia to persist in worms while treated with antibiotic. To our knowledge, these clusters have not been previously described and may be the source of the Wolbachia rebound.
Collapse
Affiliation(s)
- Emma L. Gunderson
- Dept. of Pharmaceutical Chemistry; University of California, San Francisco; San Francisco, California, United States of America
| | - Ian Vogel
- Dept. of Pharmaceutical Chemistry; University of California, San Francisco; San Francisco, California, United States of America
| | - Laura Chappell
- Dept. of Molecular, Cell and Developmental Biology; University of California, Santa Cruz; Santa Cruz, California, United States of America
| | - Christina A. Bulman
- Dept. of Pharmaceutical Chemistry; University of California, San Francisco; San Francisco, California, United States of America
| | - K. C. Lim
- Dept. of Pharmaceutical Chemistry; University of California, San Francisco; San Francisco, California, United States of America
| | - Mona Luo
- Dept. of Pharmaceutical Chemistry; University of California, San Francisco; San Francisco, California, United States of America
| | - Jeffrey D. Whitman
- Dept. of Laboratory Medicine; University of California, San Francisco; San Francisco, California, United States of America
| | - Chris Franklin
- Dept. of Pharmaceutical Chemistry; University of California, San Francisco; San Francisco, California, United States of America
| | - Young-Jun Choi
- Division of Infectious Diseases; Washington University School of Medicine, St. Louis; St. Louis, Missouri, United States of America
| | - Emilie Lefoulon
- Molecular Parasitology Division; New England BioLabs; Ipswich, Massachusetts, United States of America
| | - Travis Clark
- Veterinary Pathobiology; University of Missouri-Columbia; Columbia, Missouri, United States of America
| | - Brenda Beerntsen
- Veterinary Pathobiology; University of Missouri-Columbia; Columbia, Missouri, United States of America
| | - Barton Slatko
- Molecular Parasitology Division; New England BioLabs; Ipswich, Massachusetts, United States of America
| | - Makedonka Mitreva
- Division of Infectious Diseases; Washington University School of Medicine, St. Louis; St. Louis, Missouri, United States of America
| | - William Sullivan
- Dept. of Molecular, Cell and Developmental Biology; University of California, Santa Cruz; Santa Cruz, California, United States of America
| | - Judy A. Sakanari
- Dept. of Pharmaceutical Chemistry; University of California, San Francisco; San Francisco, California, United States of America
| |
Collapse
|
5
|
Rational Design of an Activatable Reporter for Quantitative Imaging of RNA Aberrant Splicing In Vivo. MOLECULAR THERAPY-METHODS & CLINICAL DEVELOPMENT 2020; 17:904-911. [PMID: 32405512 PMCID: PMC7210378 DOI: 10.1016/j.omtm.2020.04.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Accepted: 04/13/2020] [Indexed: 02/02/2023]
Abstract
Pre-mRNA splicing, the process of removing introns from pre-mRNA and the arrangement of exons to produce mature transcripts, is a crucial step in the expression of most eukaryote genes. However, the splicing kinetics remain poorly characterized in living cells, mainly because current methods cannot provide the dynamic information of splicing events. Here, we developed a genetically encoded bioluminescence reporter for real-time imaging of the pre-mRNA splicing process in living subjects. We showed that the bioluminescence reporter is able to visualize the pre-mRNA aberrant splicing process in living cells in a dose- and time-dependent manner. Moreover, this reporter could provide quantitative and longitudinal information of splicing activity in response to exogenous splicing inhibitors in living animals. Our data suggest that this activatable reporter could serve as a promising tool for the high-throughput screening of splicing modulators, which would facilitate the drug development for human diseases caused by the abnormal splicing of mRNA.
Collapse
|
6
|
Koscielniak D, Wons E, Wilkowska K, Sektas M. Non-programmed transcriptional frameshifting is common and highly RNA polymerase type-dependent. Microb Cell Fact 2018; 17:184. [PMID: 30474557 PMCID: PMC6260861 DOI: 10.1186/s12934-018-1034-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Accepted: 11/19/2018] [Indexed: 12/15/2022] Open
Abstract
Background The viral or host systems for a gene expression assume repeatability of the process and high quality of the protein product. Since level and fidelity of transcription primarily determines the overall efficiency, all factors contributing to their decrease should be identified and optimized. Among many observed processes, non-programmed insertion/deletion (indel) of nucleotide during transcription (slippage) occurring at homopolymeric A/T sequences within a gene can considerably impact its expression. To date, no comparative study of the most utilized Escherichia coli and T7 bacteriophage RNA polymerases (RNAP) propensity for this type of erroneous mRNA synthesis has been reported. To address this issue we evaluated the influence of shift-prone A/T sequences by assessing indel-dependent phenotypic changes. RNAP-specific expression profile was examined using two of the most potent promoters, ParaBAD of E. coli and φ10 of phage T7. Results Here we report on the first systematic study on requirements for efficient transcriptional slippage by T7 phage and cellular RNAPs considering three parameters: homopolymer length, template type, and frameshift directionality preferences. Using a series of out-of-frame gfp reporter genes fused to a variety of A/T homopolymeric sequences we show that T7 RNAP has an exceptional potential for generating frameshifts and is capable of slipping on as few as three adenine or four thymidine residues in a row, in a flanking sequence-dependent manner. In contrast, bacterial RNAP exhibits a relatively low ability to baypass indel mutations and requires a run of at least 7 tymidine and even more adenine residues. This difference comes from involvement of various intrinsic proofreading properties. Our studies demonstrate distinct preference towards a specific homopolymer in slippage induction. Whereas insertion slippage performed by T7 RNAP (but not deletion) occurs tendentiously on poly(A) rather than on poly(T) runs, strong bias towards poly(T) for the host RNAP is observed. Conclusions Intrinsic RNAP slippage properties involve trade-offs between accuracy, speed and processivity of transcription. Viral T7 RNAP manifests far greater inclinations to the transcriptional slippage than E. coli RNAP. This possibly plays an important role in driving bacteriophage adaptation and therefore could be considered as beneficial. However, from biotechnological and experimental viewpoint, this might create some problems, and strongly argues for employing bacterial expression systems, stocked with proofreading mechanisms. Electronic supplementary material The online version of this article (10.1186/s12934-018-1034-4) contains supplementary material, which is available to authorized users.
Collapse
Affiliation(s)
- Dawid Koscielniak
- Department of Microbiology, Faculty of Biology, University of Gdansk, Wita Stwosza 59, 80-308, Gdansk, Poland
| | - Ewa Wons
- Department of Microbiology, Faculty of Biology, University of Gdansk, Wita Stwosza 59, 80-308, Gdansk, Poland
| | - Karolina Wilkowska
- Department of Microbiology, Faculty of Biology, University of Gdansk, Wita Stwosza 59, 80-308, Gdansk, Poland
| | - Marian Sektas
- Department of Microbiology, Faculty of Biology, University of Gdansk, Wita Stwosza 59, 80-308, Gdansk, Poland.
| |
Collapse
|
7
|
Wons E, Koscielniak D, Szadkowska M, Sektas M. Evaluation of GFP reporter utility for analysis of transcriptional slippage during gene expression. Microb Cell Fact 2018; 17:150. [PMID: 30241530 PMCID: PMC6149199 DOI: 10.1186/s12934-018-0999-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2018] [Accepted: 09/17/2018] [Indexed: 11/20/2022] Open
Abstract
Background Epimutations arising from transcriptional slippage seem to have more important role in regulating gene expression than earlier though. Since the level and the fidelity of transcription primarily determine the overall efficiency of gene expression, all factors contributing to their decrease should be identified and optimized. Results To examine the influence of A/T homopolymeric sequences on introduction of erroneous nucleotides by slippage mechanism green fluorescence protein (GFP) reporter was chosen. The in- or out-of-frame gfp gene was fused to upstream fragment with variable number of adenine or thymine stretches resulting in several hybrid GFP proteins with diverse amino acids at N-terminus. Here, by using T7 phage expression system we showed that the intensity of GFP fluorescence mainly depends on the number of the retained natural amino acids. While the lack of serine (S2) residue results in negligible effects, the lack of serine and lysine (S2K3) contributed to a significant reduction in fluorescence by 2.7-fold for polyA-based in-frame controls and twofold for polyTs. What is more, N-terminal tails amino acid composition was rather of secondary importance, since the whole-cell fluorescence differed in a range of 9–18% between corresponding polyA- and polyT-based constructs. Conclusions Here we present experimental evidence for utility of GFP reporter for accurate estimation of A/T homopolymeric sequence contribution in transcriptional slippage induction. We showed that the intensity of GFP hybrid fluorescence mainly depends on the number of retained natural amino acids, thus fluorescence raw data need to be referred to appropriate positive control. Moreover, only in case of GFP hybrids with relatively short N-terminal tags the fluorescence level solely reflects production yield, what further indicates the impact of an individual slippage sequence. Our results demonstrate that in contrast to the E. coli enzyme, T7 RNA polymerase exhibits extremely high propensity to slippage even on runs as short as 3 adenine or 4 thymine residues. Electronic supplementary material The online version of this article (10.1186/s12934-018-0999-3) contains supplementary material, which is available to authorized users.
Collapse
Affiliation(s)
- Ewa Wons
- Department of Microbiology, University of Gdansk, Wita Stwosza 59, 80-308, Gdansk, Poland
| | - Dawid Koscielniak
- Department of Microbiology, University of Gdansk, Wita Stwosza 59, 80-308, Gdansk, Poland
| | - Monika Szadkowska
- Department of Microbiology, University of Gdansk, Wita Stwosza 59, 80-308, Gdansk, Poland
| | - Marian Sektas
- Department of Microbiology, University of Gdansk, Wita Stwosza 59, 80-308, Gdansk, Poland.
| |
Collapse
|
8
|
Penno C, Kumari R, Baranov PV, van Sinderen D, Atkins JF. Specific reverse transcriptase slippage at the HIV ribosomal frameshift sequence: potential implications for modulation of GagPol synthesis. Nucleic Acids Res 2017; 45:10156-10167. [PMID: 28973470 PMCID: PMC5737442 DOI: 10.1093/nar/gkx690] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2017] [Accepted: 07/24/2017] [Indexed: 12/28/2022] Open
Abstract
Synthesis of HIV GagPol involves a proportion of ribosomes translating a U6A shift site at the distal end of the gag gene performing a programmed -1 ribosomal frameshift event to enter the overlapping pol gene. In vitro studies here show that at the same shift motif HIV reverse transcriptase generates -1 and +1 indels with their ratio being sensitive to the relative concentration ratio of dNTPs specified by the RNA template slippage-prone sequence and its 5' adjacent base. The GGG sequence 3' adjacent to the U6A shift/slippage site, which is important for ribosomal frameshifting, is shown here to limit reverse transcriptase base substitution and indel 'errors' in the run of A's in the product. The indels characterized here have either 1 more or less A, than the corresponding number of template U's. cDNA with 5 A's may yield novel Gag product(s), while cDNA with an extra base, 7 A's, may only be a minor contributor to GagPol polyprotein. Synthesis of a proportion of non-ribosomal frameshift derived GagPol would be relevant in efforts to identify therapeutically useful compounds that perturb the ratio of GagPol to Gag, and pertinent to the extent in which specific polymerase slippage is utilized in gene expression.
Collapse
Affiliation(s)
- Christophe Penno
- School of Biochemistry, University College Cork, Cork, Ireland.,School of Microbiology, University College Cork, Cork, Ireland.,Alimentary Pharmabiotic Centre, University College Cork, Cork, Ireland
| | - Romika Kumari
- School of Biochemistry, University College Cork, Cork, Ireland
| | - Pavel V Baranov
- School of Biochemistry, University College Cork, Cork, Ireland
| | - Douwe van Sinderen
- School of Microbiology, University College Cork, Cork, Ireland.,Alimentary Pharmabiotic Centre, University College Cork, Cork, Ireland
| | - John F Atkins
- School of Biochemistry, University College Cork, Cork, Ireland.,School of Microbiology, University College Cork, Cork, Ireland.,Department of Human Genetics, University of Utah, Salt Lake City, UT 84112-5330, USA
| |
Collapse
|
9
|
Wernegreen JJ. Ancient bacterial endosymbionts of insects: Genomes as sources of insight and springboards for inquiry. Exp Cell Res 2017; 358:427-432. [DOI: 10.1016/j.yexcr.2017.04.028] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Revised: 04/24/2017] [Accepted: 04/25/2017] [Indexed: 01/20/2023]
|
10
|
Kim D, Thairu MW, Hansen AK. Novel Insights into Insect-Microbe Interactions-Role of Epigenomics and Small RNAs. FRONTIERS IN PLANT SCIENCE 2016; 7:1164. [PMID: 27540386 PMCID: PMC4972996 DOI: 10.3389/fpls.2016.01164] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Accepted: 07/20/2016] [Indexed: 05/23/2023]
Abstract
It has become increasingly clear that microbes form close associations with the vast majority of animal species, especially insects. In fact, an array of diverse microbes is known to form shared metabolic pathways with their insect hosts. A growing area of research in insect-microbe interactions, notably for hemipteran insects and their mutualistic symbionts, is to elucidate the regulation of this inter-domain metabolism. This review examines two new emerging mechanisms of gene regulation and their importance in host-microbe interactions. Specifically, we highlight how the incipient areas of research on regulatory "dark matter" such as epigenomics and small RNAs, can play a pivotal role in the evolution of both insect and microbe gene regulation. We then propose specific models of how these dynamic forms of gene regulation can influence insect-symbiont-plant interactions. Future studies in this area of research will give us a systematic understanding of how these symbiotic microbes and animals reciprocally respond to and regulate their shared metabolic processes.
Collapse
|
11
|
Ivancic-Jelecki J, Slovic A, Šantak M, Tešović G, Forcic D. Common position of indels that cause deviations from canonical genome organization in different measles virus strains. Virol J 2016; 13:134. [PMID: 27473517 PMCID: PMC4966754 DOI: 10.1186/s12985-016-0587-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Accepted: 07/21/2016] [Indexed: 12/15/2022] Open
Abstract
BACKGROUND The canonical genome organization of measles virus (MV) is characterized by total size of 15 894 nucleotides (nts) and defined length of every genomic region, both coding and non-coding. Only rarely have reports of strains possessing non-canonical genomic properties (possessing indels, with or without the change of total genome length) been published. The observed mutations are mutually compensatory in a sense that the total genome length remains polyhexameric. Although programmed and highly precise pseudo-templated nucleotide additions during transcription are inherent to polymerases of all viruses belonging to family Paramyxoviridae, a similar mechanism that would serve to non-randomly correct genome length, if an indel has occurred during replication, has so far not been described in the context of a complete virus genome. METHODS We compiled all complete MV genomic sequences (64 in total) available in open access sequence databases. Multiple sequence comparisons and phylogenetic analyses were performed with the aim of exploring whether non-recombinant and non-evolutionary linked measles strains that show deviations from canonical genome organization possess a common genetic characteristic. RESULTS In 11 MV sequences we detected deviations from canonical genome organization due to short indels located within homopolymeric stretches or next to them. In nine out of 11 identified non-canonical MV sequences, a common feature was observed: one mutation, either an insertion or a deletion, was located in a 28 nts long region in F gene 5' untranslated region (positions 5051-5078 in genomic cDNA of canonical strains). This segment is composed of five tandemly linked homopolymeric stretches, its consensus sequence is G6-7C7-8A6-7G1-3C5-6. Although none of the mononucleotide repeats within this segment has fixed length, the total number of nts in canonical strains is always 28. These nine non-canonical strains, as well as the tenth (not mutated in 5051-5078 segment), can be grouped in three clusters, based on their passage histories/epidemiological data/genetic similarities. There are no indications that the 3 clusters are evolutionary linked, other than the fact that they all belong to clade D. CONCLUSIONS A common narrow genomic region was found to be mutated in different, non-related, wild type strains suggesting that this region might have a function in non-random genome length corrections occurring during MV replication.
Collapse
Affiliation(s)
- Jelena Ivancic-Jelecki
- University of Zagreb, Centre for research and knowledge transfer in biotechnology, Rockefellerova 10, 10 000 Zagreb, Croatia
- Center of Excellence for Viral Immunology and Vaccines, CERVirVac, Zagreb, Croatia
| | - Anamarija Slovic
- University of Zagreb, Centre for research and knowledge transfer in biotechnology, Rockefellerova 10, 10 000 Zagreb, Croatia
- Center of Excellence for Viral Immunology and Vaccines, CERVirVac, Zagreb, Croatia
| | - Maja Šantak
- University of Zagreb, Centre for research and knowledge transfer in biotechnology, Rockefellerova 10, 10 000 Zagreb, Croatia
- Center of Excellence for Viral Immunology and Vaccines, CERVirVac, Zagreb, Croatia
| | - Goran Tešović
- Pediatric infectious diseases department, University hospital for infectious diseases “Dr. Fran Mihaljevic”, Mirogojska 8, 10 000 Zagreb, Croatia
| | - Dubravko Forcic
- University of Zagreb, Centre for research and knowledge transfer in biotechnology, Rockefellerova 10, 10 000 Zagreb, Croatia
- Center of Excellence for Viral Immunology and Vaccines, CERVirVac, Zagreb, Croatia
| |
Collapse
|
12
|
de Miranda NFCC, van Dinther M, van den Akker BEWM, van Wezel T, ten Dijke P, Morreau H. Transforming Growth Factor β Signaling in Colorectal Cancer Cells With Microsatellite Instability Despite Biallelic Mutations in TGFBR2. Gastroenterology 2015; 148:1427-37.e8. [PMID: 25736321 DOI: 10.1053/j.gastro.2015.02.052] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/01/2014] [Revised: 02/24/2015] [Accepted: 02/26/2015] [Indexed: 02/07/2023]
Abstract
BACKGROUND & AIMS Most colorectal cancer (CRC) cells with high levels of microsatellite instability (MSI-H) accumulate mutations at a microsatellite sequence in the gene encoding transforming growth factor β receptor II (TGFBR2). TGFβ signaling therefore is believed to be defective in these tumors, although CRC cells with TGFBR2 mutations have been reported to remain sensitive to TGFβ. We investigated how TGFβ signaling might continue in MSI-H CRC cells. METHODS We sequenced the 10-adenines microsatellite sequence in the TGFBR2 gene of 32 MSI-H colon cancer tissues and 6 cell lines (HCT116, LS180, LS411N, RKO, SW48, and SW837). Activation of TGFβ signaling was detected by SMAD2 phosphorylation and through use of a TGFβ-responsive reporter construct in all CRC cell lines. Transcripts of TGFBR2 were knocked-down in CRC cells using short hairpin RNA. Full-length and mutant forms of TGFBR2 were expressed in LS411N cells, which do not respond to TGFβ, and their activities were measured. RESULTS SMAD2 was phosphorylated in most MSI-H CRC tissues (strong detection in 44% and weak detection in 34% of MSI-H tumors). Phosphorylation of SMAD2 in MSI-H cells required TGFBR2—even the form encoding a frameshift mutation. Transcription and translation of TGFBR2 with a 1-nucleotide deletion at its microsatellite sequence still produced a full-length TGFBR2 protein. However, protein expression required preservation of the TGFBR2 microsatellite sequence; cells in which this sequence was replaced with a synonymous nonmicrosatellite sequence did not produce functional TGFBR2 protein. CONCLUSION TGFβ signaling remains active in some MSI-H CRC cells despite the presence of frameshift mutations in the TGFBR2 gene because the mutated gene still expresses a functional protein. Strategies to reactivate TGFβ signaling in colorectal tumors might not be warranted, and the functional effects of mutations at other regions of microsatellite instability should be evaluated.
Collapse
Affiliation(s)
| | - Maarten van Dinther
- Department of Molecular Cell Biology, Cancer Genomics Centre Netherlands, Leiden University Medical Center, Leiden, The Netherlands
| | | | - Tom van Wezel
- Department of Pathology, Leiden University Medical Center, Leiden, The Netherlands
| | - Peter ten Dijke
- Department of Molecular Cell Biology, Cancer Genomics Centre Netherlands, Leiden University Medical Center, Leiden, The Netherlands; Ludwig Institute for Cancer Research, Science for Life Laboratory, Uppsala University, Uppsala, Sweden.
| | - Hans Morreau
- Department of Pathology, Leiden University Medical Center, Leiden, The Netherlands.
| |
Collapse
|
13
|
Lin WH, Rocco MJ, Bertozzi-Villa A, Kussell E. Populations adapt to fluctuating selection using derived and ancestral allelic diversity. Evolution 2015; 69:1448-1460. [PMID: 25908222 DOI: 10.1111/evo.12665] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2014] [Accepted: 04/08/2015] [Indexed: 12/22/2022]
Abstract
Populations can adapt to changing environments by using allelic diversity, yet whether diversity is recently derived or ancestral is often debated. Although evolution could productively use both types of diversity in a changing environment, their relative frequency has not been quantified. We address this question experimentally using budding yeast strains that harbor a tandem repeat containing URA3 gene, which we expose to cyclical selection and counterselection. We characterize and quantify the dynamics of frameshift events in the URA3 gene in eight populations over 12 cycles of selection and find that ancestral alleles account for 10-20% of all adaptive events. Using a general model of fluctuating selection, we determine how these results depend on mutation rates, population sizes, and fluctuation timescales. We quantify the contribution of derived alleles to the adaptation process using the de novo mutation rate along the population's ancestral lineage, a novel measure that is applicable in a wide range of settings. We find that the adaptive dynamics undergoes a sharp transition from selection on ancestral alleles to selection on derived alleles as fluctuation timescales increase. Our results demonstrate that fluctuations can select between different modes of adaptation over evolutionary timescales.
Collapse
Affiliation(s)
- Wei-Hsiang Lin
- Department of Biology, Center for Genomics and Systems Biology, New York University, New York, New York, 10003
| | - Mark J Rocco
- Department of Biology, Center for Genomics and Systems Biology, New York University, New York, New York, 10003
| | - Amelia Bertozzi-Villa
- Department of Biology, Center for Genomics and Systems Biology, New York University, New York, New York, 10003
| | - Edo Kussell
- Department of Biology, Center for Genomics and Systems Biology, New York University, New York, New York, 10003.,Department of Physics, New York University, New York, New York, 10003
| |
Collapse
|
14
|
Productive mRNA stem loop-mediated transcriptional slippage: Crucial features in common with intrinsic terminators. Proc Natl Acad Sci U S A 2015; 112:E1984-93. [PMID: 25848054 DOI: 10.1073/pnas.1418384112] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Escherichia coli and yeast DNA-dependent RNA polymerases are shown to mediate efficient nascent transcript stem loop formation-dependent RNA-DNA hybrid realignment. The realignment was discovered on the heteropolymeric sequence T5C5 and yields transcripts lacking a C residue within a corresponding U5C4. The sequence studied is derived from a Roseiflexus insertion sequence (IS) element where the resulting transcriptional slippage is required for transposase synthesis. The stability of the RNA structure, the proximity of the stem loop to the slippage site, the length and composition of the slippage site motif, and the identity of its 3' adjacent nucleotides (nt) are crucial for transcripts lacking a single C. In many respects, the RNA structure requirements for this slippage resemble those for hairpin-dependent transcription termination. In a purified in vitro system, the slippage efficiency ranges from 5% to 75% depending on the concentration ratios of the nucleotides specified by the slippage sequence and the 3' nt context. The only previous proposal of stem loop mediated slippage, which was in Ebola virus expression, was based on incorrect data interpretation. We propose a mechanical slippage model involving the RNAP translocation state as the main motor in slippage directionality and efficiency. It is distinct from previously described models, including the one proposed for paramyxovirus, where following random movement efficiency is mainly dependent on the stability of the new realigned hybrid. In broadening the scope for utilization of transcription slippage for gene expression, the stimulatory structure provides parallels with programmed ribosomal frameshifting at the translation level.
Collapse
|
15
|
Williams LE, Wernegreen JJ. Genome evolution in an ancient bacteria-ant symbiosis: parallel gene loss among Blochmannia spanning the origin of the ant tribe Camponotini. PeerJ 2015; 3:e881. [PMID: 25861561 PMCID: PMC4389277 DOI: 10.7717/peerj.881] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2014] [Accepted: 03/18/2015] [Indexed: 12/11/2022] Open
Abstract
Stable associations between bacterial endosymbionts and insect hosts provide opportunities to explore genome evolution in the context of established mutualisms and assess the roles of selection and genetic drift across host lineages and habitats. Blochmannia, obligate endosymbionts of ants of the tribe Camponotini, have coevolved with their ant hosts for ∼40 MY. To investigate early events in Blochmannia genome evolution across this ant host tribe, we sequenced Blochmannia from two divergent host lineages, Colobopsis obliquus and Polyrhachis turneri, and compared them with four published genomes from Blochmannia of Camponotus sensu stricto. Reconstructed gene content of the last common ancestor (LCA) of these six Blochmannia genomes is reduced (690 protein coding genes), consistent with rapid gene loss soon after establishment of the symbiosis. Differential gene loss among Blochmannia lineages has affected cellular functions and metabolic pathways, including DNA replication and repair, vitamin biosynthesis and membrane proteins. Blochmannia of P. turneri (i.e., B. turneri) encodes an intact DnaA chromosomal replication initiation protein, demonstrating that loss of dnaA was not essential for establishment of the symbiosis. Based on gene content, B. obliquus and B. turneri are unable to provision hosts with riboflavin. Of the six sequenced Blochmannia, B. obliquus is the earliest diverging lineage (i.e., the sister group of other Blochmannia sampled) and encodes the fewest protein-coding genes and the most pseudogenes. We identified 55 genes involved in parallel gene loss, including glutamine synthetase, which may participate in nitrogen recycling. Pathways for biosynthesis of coenzyme A, terpenoids and riboflavin were lost in multiple lineages, suggesting relaxed selection on the pathway after inactivation of one component. Analysis of Illumina read datasets did not detect evidence of plasmids encoding missing functions, nor the presence of coresident symbionts other than Wolbachia. Although gene order is strictly conserved in four Blochmannia of Camponotus sensu stricto, comparisons with deeply divergent lineages revealed inversions in eight genomic regions, indicating ongoing recombination despite ancestral loss of recA. In sum, the addition of two Blochmannia genomes of divergent host lineages enables reconstruction of early events in evolution of this symbiosis and suggests that Blochmannia lineages may experience distinct, host-associated selective pressures. Understanding how evolutionary forces shape genome reduction in this system may help to clarify forces driving gene loss in other bacteria, including intracellular pathogens.
Collapse
Affiliation(s)
- Laura E Williams
- Duke Center for Genomic and Computational Biology, Duke University , Durham, NC , USA
| | - Jennifer J Wernegreen
- Duke Center for Genomic and Computational Biology, Duke University , Durham, NC , USA ; Nicholas School of the Environment, Duke University , Durham, NC , USA
| |
Collapse
|
16
|
Wons E, Furmanek-Blaszk B, Sektas M. RNA editing by T7 RNA polymerase bypasses InDel mutations causing unexpected phenotypic changes. Nucleic Acids Res 2015; 43:3950-63. [PMID: 25824942 PMCID: PMC4417176 DOI: 10.1093/nar/gkv269] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2015] [Accepted: 03/17/2015] [Indexed: 12/26/2022] Open
Abstract
DNA-dependent T7 RNA polymerase (T7 RNAP) is the most powerful tool for both gene expression and in vitro transcription. By using a Next Generation Sequencing (NGS) approach we have analyzed the polymorphism of a T7 RNAP-generated mRNA pool of the mboIIM2 gene. We find that the enzyme displays a relatively high level of template-dependent transcriptional infidelity. The nucleotide misincorporations and multiple insertions in A/T-rich tracts of homopolymers in mRNA (0.20 and 0.089%, respectively) cause epigenetic effects with significant impact on gene expression that is disproportionally high to their frequency of appearance. The sequence-dependent rescue of single and even double InDel frameshifting mutants and wild-type phenotype recovery is observed as a result. As a consequence, a heterogeneous pool of functional and non-functional proteins of almost the same molecular mass is produced where the proteins are indistinguishable from each other upon ordinary analysis. We suggest that transcriptional infidelity as a general feature of the most effective RNAPs may serve to repair and/or modify a protein function, thus increasing the repertoire of phenotypic variants, which in turn has a high evolutionary potential.
Collapse
Affiliation(s)
- Ewa Wons
- Department of Microbiology, University of Gdansk, Gdansk 80-308, Poland
| | | | - Marian Sektas
- Department of Microbiology, University of Gdansk, Gdansk 80-308, Poland
| |
Collapse
|
17
|
Gueguen E, Wills NM, Atkins JF, Cascales E. Transcriptional frameshifting rescues Citrobacter rodentium type VI secretion by the production of two length variants from the prematurely interrupted tssM gene. PLoS Genet 2014; 10:e1004869. [PMID: 25474156 PMCID: PMC4256274 DOI: 10.1371/journal.pgen.1004869] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Accepted: 11/03/2014] [Indexed: 11/30/2022] Open
Abstract
The Type VI secretion system (T6SS) mediates toxin delivery into both eukaryotic and prokaryotic cells. It is composed of a cytoplasmic structure resembling the tail of contractile bacteriophages anchored to the cell envelope through a membrane complex composed of the TssL and TssM inner membrane proteins and of the TssJ outer membrane lipoprotein. The C-terminal domain of TssM is required for its interaction with TssJ, and for the function of the T6SS. In Citrobacter rodentium, the tssM1 gene does not encode the C-terminal domain. However, the stop codon is preceded by a run of 11 consecutive adenosines. In this study, we demonstrate that this poly-A tract is a transcriptional slippery site that induces the incorporation of additional adenosines, leading to frameshifting, and hence the production of two TssM1 variants, including a full-length canonical protein. We show that both forms of TssM1, and the ratio between these two forms, are required for the function of the T6SS in C. rodentium. Finally, we demonstrate that the tssM gene associated with the Yersinia pseudotuberculosis T6SS-3 gene cluster is also subjected to transcriptional frameshifting. Nonstandard decoding mechanisms lead to the synthesis of different protein variants from a single DNA sequence. These mechanisms are particularly important when the genome length has to be limited such as viral genomes, limited by the available space in the capsid, or to synthesize two different polypeptides that have distinct functional properties. Here, we report that tssM, a gene encoded within the Citrobacter rodentium Type VI secretion (T6S) gene cluster, is interrupted by a premature stop codon; however, the stop codon is preceded by a slippery site constituted by 11 consecutive adenosines. Reiterative transcription leads to the incorporation of additional nucleotides in the mRNA and therefore restores the original framing. As a consequence, two different TssM variants are created by transcriptional frameshifting, including a full-length 130-kDa protein and an 88-kDa truncated variant. We further show that both forms, and the ratio between these two forms, are required for the function of the transport apparatus. Interestingly, a similar mechanism regulates the synthesis of two TssM variants in Yersinia pseudotuberculosis.
Collapse
Affiliation(s)
- Erwan Gueguen
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM), Institut de Microbiologie de la Méditerranée, CNRS – Aix-Marseille Université, UMR 7255, Marseille, France
- * E-mail: (EG); (EC)
| | - Norma M. Wills
- Department of Human Genetics, University of Utah, Salt Lake City, Utah, United States of America
| | - John F. Atkins
- Department of Human Genetics, University of Utah, Salt Lake City, Utah, United States of America
- Departments of Biochemistry and Microbiology, University College Cork, Cork, Ireland
| | - Eric Cascales
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM), Institut de Microbiologie de la Méditerranée, CNRS – Aix-Marseille Université, UMR 7255, Marseille, France
- * E-mail: (EG); (EC)
| |
Collapse
|
18
|
Rosas-Pérez T, Rosenblueth M, Rincón-Rosales R, Mora J, Martínez-Romero E. Genome sequence of "Candidatus Walczuchella monophlebidarum" the flavobacterial endosymbiont of Llaveia axin axin (Hemiptera: Coccoidea: Monophlebidae). Genome Biol Evol 2014; 6:714-26. [PMID: 24610838 PMCID: PMC3971599 DOI: 10.1093/gbe/evu049] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Scale insects (Hemiptera: Coccoidae) constitute a very diverse group of sap-feeding insects with a large diversity of symbiotic associations with bacteria. Here, we present the complete genome sequence, metabolic reconstruction, and comparative genomics of the flavobacterial endosymbiont of the giant scale insect Llaveia axin axin. The gene repertoire of its 309,299 bp genome was similar to that of other flavobacterial insect endosymbionts though not syntenic. According to its genetic content, essential amino acid biosynthesis is likely to be the flavobacterial endosymbiont's principal contribution to the symbiotic association with its insect host. We also report the presence of a γ-proteobacterial symbiont that may be involved in waste nitrogen recycling and also has amino acid biosynthetic capabilities that may provide metabolic precursors to the flavobacterial endosymbiont. We propose “Candidatus Walczuchella monophlebidarum” as the name of the flavobacterial endosymbiont of insects from the Monophlebidae family.
Collapse
Affiliation(s)
- Tania Rosas-Pérez
- Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
| | | | | | | | | |
Collapse
|
19
|
Repetitive sequence variations in the promoter region of the adhesin-encoding gene sabA of Helicobacter pylori affect transcription. J Bacteriol 2014; 196:3421-9. [PMID: 25022855 DOI: 10.1128/jb.01956-14] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
The pathogenesis of diseases elicited by the gastric pathogen Helicobacter pylori is partially determined by the effectiveness of adaptation to the variably acidic environment of the host stomach. Adaptation includes appropriate adherence to the gastric epithelium via outer membrane protein adhesins such as SabA. The expression of sabA is subject to regulation via phase variation in the promoter and coding regions as well as repression by the two-component system ArsRS. In this study, we investigated the role of a homopolymeric thymine [poly(T)] tract -50 to -33 relative to the sabA transcriptional start site in H. pylori strain J99. We quantified sabA expression in H. pylori J99 by quantitative reverse transcription-PCR (RT-PCR), demonstrating significant changes in sabA expression associated with experimental manipulations of poly(T) tract length. Mimicking the length increase of this tract by adding adenines instead of thymines had similar effects, while the addition of other nucleotides failed to affect sabA expression in the same manner. We hypothesize that modification of the poly(T) tract changes DNA topology, affecting regulatory protein interaction(s) or RNA polymerase binding efficiency. Additionally, we characterized the interaction between the sabA promoter region and ArsR, a response regulator affecting sabA expression. Using recombinant ArsR in electrophoretic mobility shift assays (EMSA), we localized binding to a sequence with partial dyad symmetry -20 and +38 relative to the sabA +1 site. The control of sabA expression by both ArsRS and phase variation at two distinct repeat regions suggests the control of sabA expression is both complex and vital to H. pylori infection.
Collapse
|
20
|
Wild-type measles viruses with non-standard genome lengths. PLoS One 2014; 9:e95470. [PMID: 24748123 PMCID: PMC3991672 DOI: 10.1371/journal.pone.0095470] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Accepted: 03/27/2014] [Indexed: 12/13/2022] Open
Abstract
The length of the single stranded, negative sense RNA genome of measles virus (MeV) is highly conserved at 15,894 nucleotides (nt). MeVs can be grouped into 24 genotypes based on the highly variable 450 nucleotides coding for the carboxyl-terminus of the nucleocapsid protein (N-450). Here, we report the genomic sequences of 2 wild-type viral isolates of genotype D4 with genome lengths of 15,900 nt. Both genomes had a 7 nt insertion in the 3′ untranslated region (UTR) of the matrix (M) gene and a 1 nt deletion in the 5′ UTR of the fusion (F) gene. The net gain of 6 nt complies with the rule-of-six required for replication competency of the genomes of morbilliviruses. The insertions and deletion (indels) were confirmed in a patient sample that was the source of one of the viral isolates. The positions of the indels were identical in both viral isolates, even though epidemiological data and the 3 nt differences in N-450 between the two genomes suggested that the viruses represented separate chains of transmission. Identical indels were found in the M-F intergenic regions of 14 additional genotype D4 viral isolates that were imported into the US during 2007–2010. Viral isolates with and without indels produced plaques of similar size and replicated efficiently in A549/hSLAM and Vero/hSLAM cells. This is the first report of wild-type MeVs with genome lengths other than 15,894 nt and demonstrates that the length of the M-F UTR of wild-type MeVs is flexible.
Collapse
|
21
|
Rockah-Shmuel L, Tóth-Petróczy Á, Sela A, Wurtzel O, Sorek R, Tawfik DS. Correlated occurrence and bypass of frame-shifting insertion-deletions (InDels) to give functional proteins. PLoS Genet 2013; 9:e1003882. [PMID: 24204297 PMCID: PMC3812077 DOI: 10.1371/journal.pgen.1003882] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2013] [Accepted: 09/02/2013] [Indexed: 11/19/2022] Open
Abstract
Short insertions and deletions (InDels) comprise an important part of the natural mutational repertoire. InDels are, however, highly deleterious, primarily because two-thirds result in frame-shifts. Bypass through slippage over homonucleotide repeats by transcriptional and/or translational infidelity is known to occur sporadically. However, the overall frequency of bypass and its relation to sequence composition remain unclear. Intriguingly, the occurrence of InDels and the bypass of frame-shifts are mechanistically related - occurring through slippage over repeats by DNA or RNA polymerases, or by the ribosome, respectively. Here, we show that the frequency of frame-shifting InDels, and the frequency by which they are bypassed to give full-length, functional proteins, are indeed highly correlated. Using a laboratory genetic drift, we have exhaustively mapped all InDels that occurred within a single gene. We thus compared the naive InDel repertoire that results from DNA polymerase slippage to the frame-shifting InDels tolerated following selection to maintain protein function. We found that InDels repeatedly occurred, and were bypassed, within homonucleotide repeats of 3–8 bases. The longer the repeat, the higher was the frequency of InDels formation, and the more frequent was their bypass. Besides an expected 8A repeat, other types of repeats, including short ones, and G and C repeats, were bypassed. Although obtained in vitro, our results indicate a direct link between the genetic occurrence of InDels and their phenotypic rescue, thus suggesting a potential role for frame-shifting InDels as bridging evolutionary intermediates. Homonucleotide repeats are exceptionally prone to insertions and/or deletions of bases (InDels). However, unless they occur in a multiplicity of 3 bases, InDels disrupt the reading frame and are thus expected to be purged from coding regions. Homonucleotide repeats, however, are also vulnerable to slippage by RNA polymerases and the ribosome. Using laboratory evolution techniques, we systematically mapped the occurrence of InDels within a given gene, before and after selection. Our data indicate that frame-shifting InDels were frequently bypassed to give functional proteins at surprisingly high frequencies. Further, we found a strict correlation between the repeat length, the frequency of occurrence of InDels at the DNA level, and the likelihood of bypass by transcriptional/translational slippage. Our results suggest that frame-shifting InDels might comprise functional evolutionary intermediates, and an effective mean of sequence divergence (e.g. when an adjacent InDel restores the frame, resulting in altered sequence and, potentially, in an altered protein structure).
Collapse
Affiliation(s)
- Liat Rockah-Shmuel
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot, Israel
| | - Ágnes Tóth-Petróczy
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot, Israel
| | - Asaf Sela
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot, Israel
| | - Omri Wurtzel
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Rotem Sorek
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Dan S. Tawfik
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot, Israel
- * E-mail:
| |
Collapse
|
22
|
Antonov I, Coakley A, Atkins JF, Baranov PV, Borodovsky M. Identification of the nature of reading frame transitions observed in prokaryotic genomes. Nucleic Acids Res 2013; 41:6514-30. [PMID: 23649834 PMCID: PMC3711429 DOI: 10.1093/nar/gkt274] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Our goal was to identify evolutionary conserved frame transitions in protein coding regions and to uncover an underlying functional role of these structural aberrations. We used the ab initio frameshift prediction program, GeneTack, to detect reading frame transitions in 206 991 genes (fs-genes) from 1106 complete prokaryotic genomes. We grouped 102 731 fs-genes into 19 430 clusters based on sequence similarity between protein products (fs-proteins) as well as conservation of predicted position of the frameshift and its direction. We identified 4010 pseudogene clusters and 146 clusters of fs-genes apparently using recoding (local deviation from using standard genetic code) due to possessing specific sequence motifs near frameshift positions. Particularly interesting was finding of a novel type of organization of the dnaX gene, where recoding is required for synthesis of the longer subunit, τ. We selected 20 clusters of predicted recoding candidates and designed a series of genetic constructs with a reporter gene or affinity tag whose expression would require a frameshift event. Expression of the constructs in Escherichia coli demonstrated enrichment of the set of candidates with sequences that trigger genuine programmed ribosomal frameshifting; we have experimentally confirmed four new families of programmed frameshifts.
Collapse
Affiliation(s)
- Ivan Antonov
- School of Computational Science and Engineering at Georgia Tech, Atlanta, GA 30332, USA
| | | | | | | | | |
Collapse
|
23
|
Abstract
Large cell size is not restricted to a particular bacterial lifestyle, dispersal method, or cell envelope type. What is conserved among the very large bacteria are the quantity and arrangement of their genomic resources. All large bacteria described to date appear to be highly polyploid. This review focuses on Epulopiscium sp. type B, which maintains tens of thousands of genome copies throughout its life cycle. Only a tiny proportion of mother cell DNA is inherited by intracellular offspring, but surprisingly DNA replication takes place in the terminally differentiated mother cell as offspring grow. Massive polyploidy supports the acquisition of unstable genetic elements normally not seen in essential genes. Further studies of how large bacteria manage their genomic resources will provide insight into how simple cellular modifications can support unusual lifestyles and exceptional cell forms.
Collapse
Affiliation(s)
- Esther R Angert
- Department of Microbiology, Cornell University, Ithaca, New York 14853, USA.
| |
Collapse
|
24
|
Vollan HS, Tannaes T, Yamaoka Y, Bukholm G. In silico evolutionary analysis of Helicobacter pylori outer membrane phospholipase A (OMPLA). BMC Microbiol 2012; 12:206. [PMID: 22974200 PMCID: PMC3490997 DOI: 10.1186/1471-2180-12-206] [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: 02/13/2012] [Accepted: 08/31/2012] [Indexed: 01/19/2023] Open
Abstract
Background In the past decade, researchers have proposed that the pldA gene for outer membrane phospholipase A (OMPLA) is important for bacterial colonization of the human gastric ventricle. Several conserved Helicobacter pylori genes have distinct genotypes in different parts of the world, biogeographic patterns that can be analyzed through phylogenetic trees. The current study will shed light on the importance of the pldA gene in H. pylori. In silico sequence analysis will be used to investigate whether the bacteria are in the process of preserving, optimizing, or rejecting the pldA gene. The pldA gene will be phylogenetically compared to other housekeeping (HK) genes, and a possible origin via horizontal gene transfer (HGT) will be evaluated through both intra- and inter-species evolutionary analyses. Results In this study, pldA gene sequences were phylogenetically analyzed and compared with a large reference set of concatenated HK gene sequences. A total of 246 pldA nucleotide sequences were used; 207 were from Norwegian isolates, 20 were from Korean isolates, and 19 were from the NCBI database. Best-fit evolutionary models were determined with MEGA5 ModelTest for the pldA (K80 + I + G) and HK (GTR + I + G) sequences, and maximum likelihood trees were constructed. Both HK and pldA genes showed biogeographic clustering. Horizontal gene transfer was inferred based on significantly different GC contents, the codon adaptation index, and a phylogenetic conflict between a tree of OMPLA protein sequences representing 171 species and a tree of the AtpA HK protein for 169 species. Although a vast majority of the residues in OMPLA were predicted to be under purifying selection, sites undergoing positive selection were also found. Conclusions Our findings indicate that the pldA gene could have been more recently acquired than seven of the HK genes found in H. pylori. However, the common biogeographic patterns of both the HK and pldA sequences indicated that the transfer occurred long ago. Our results indicate that the bacterium is preserving the function of OMPLA, although some sites are still being evolutionarily optimized.
Collapse
Affiliation(s)
- Hilde S Vollan
- Department of Clinical Molecular Biology, Division of Medicine, Akershus University Hospital, University of Oslo, Norway.
| | | | | | | |
Collapse
|
25
|
Insight into the transmission biology and species-specific functional capabilities of tsetse (Diptera: glossinidae) obligate symbiont Wigglesworthia. mBio 2012; 3:mBio.00240-11. [PMID: 22334516 PMCID: PMC3280448 DOI: 10.1128/mbio.00240-11] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Ancient endosymbionts have been associated with extreme genome structural stability with little differentiation in gene inventory between sister species. Tsetse flies (Diptera: Glossinidae) harbor an obligate endosymbiont, Wigglesworthia, which has coevolved with the Glossina radiation. We report on the ~720-kb Wigglesworthia genome and its associated plasmid from Glossina morsitans morsitans and compare them to those of the symbiont from Glossina brevipalpis. While there was overall high synteny between the two genomes, a large inversion was noted. Furthermore, symbiont transcriptional analyses demonstrated host tissue and development-specific gene expression supporting robust transcriptional regulation in Wigglesworthia, an unprecedented observation in other obligate mutualist endosymbionts. Expression and immunohistochemistry confirmed the role of flagella during the vertical transmission process from mother to intrauterine progeny. The expression of nutrient provisioning genes (thiC and hemH) suggests that Wigglesworthia may function in dietary supplementation tailored toward host development. Furthermore, despite extensive conservation, unique genes were identified within both symbiont genomes that may result in distinct metabolomes impacting host physiology. One of these differences involves the chorismate, phenylalanine, and folate biosynthetic pathways, which are uniquely present in Wigglesworthia morsitans. Interestingly, African trypanosomes are auxotrophs for phenylalanine and folate and salvage both exogenously. It is possible that W. morsitans contributes to the higher parasite susceptibility of its host species. Genomic stasis has historically been associated with obligate endosymbionts and their sister species. Here we characterize the Wigglesworthia genome of the tsetse fly species Glossina morsitans and compare it to its sister genome within G. brevipalpis. The similarity and variation between the genomes enabled specific hypotheses regarding functional biology. Expression analyses indicate significant levels of transcriptional regulation and support development- and tissue-specific functional roles for the symbiosis previously not observed in obligate mutualist symbionts. Retention of the genetically expensive flagella within these small genomes was demonstrated to be significant in symbiont transmission and tailored to the unique tsetse fly reproductive biology. Distinctions in metabolomes were also observed. We speculate an additional role for Wigglesworthia symbiosis where infections with pathogenic trypanosomes may depend upon symbiont species-specific metabolic products and thus influence the vector competence traits of different tsetse fly host species.
Collapse
|
26
|
Eftang LL, Esbensen Y, Tannæs TM, Bukholm IRK, Bukholm G. Interleukin-8 is the single most up-regulated gene in whole genome profiling of H. pylori exposed gastric epithelial cells. BMC Microbiol 2012; 12:9. [PMID: 22248188 PMCID: PMC3292955 DOI: 10.1186/1471-2180-12-9] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2011] [Accepted: 01/17/2012] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND The association between Helicobacter pylori infection and upper gastrointestinal disease is well established. However, only a small fraction of H. pylori carriers develop disease, and there are great geographical differences in disease penetrance. The explanation to this enigma lies in the interaction between the bacterium and the host. H. pylori Outer Membrane Phospholipase A (OMPLA) has been suggested to play a role in the virulence of this bacterium. The aim of this study was to profile the most significant cellular pathways and biological processes affected in gastric epithelial cells during 24 h of H. pylori exposure, and to study the inflammatory response to OMPLA⁺ and OMPLA⁻ H. pylori variants. RESULTS Interleukin-8 was the most significantly up-regulated gene and appears to play a paramount role in the epithelial cell response to H. pylori infection and in the pathological processes leading to gastric disease. MAPK and NF-kappaB cellular pathways were powerfully activated, but did not seem to explain the impressive IL-8 response. There was marked up-regulation of TP53BP2, whose corresponding protein ASPP2 may interact with H. pylori CagA and cause marked p53 suppression of apoptosis. Other regulators of apoptosis also showed abberant regulation. We also identified up-regulation of several oncogenes and down-regulation of tumor suppressor genes as early as during the first 24 h of infection. H. pylori OMPLA phase variation did not seem to influence the inflammatory epithelial cell gene response in this experiment. CONCLUSION In whole genome analysis of the epithelial response to H. pylori exposure, IL-8 demonstrated the most marked up-regulation, and was involved in many of the most important cellular response processes to the infection. There was dysregulation of apoptosis, tumor suppressor genes and oncogenes as early as in the first 24 h of H. pylori infection, which may represent early signs of gastric tumorigenesis. OMPLA⁺/⁻ did not affect the acute inflammatory response to H. pylori.
Collapse
Affiliation(s)
- Lars L Eftang
- Department of Clinical Molecular Biology (Epigen), Institute of Clinical Medicine, University of Oslo, Akershus University Hospital, Lørenskog, Norway
- Department of Gastroenterological Surgery, Akershus University Hospital, Lørenskog, Norway
| | - Ying Esbensen
- Department of Clinical Molecular Biology (Epigen), Institute of Clinical Medicine, University of Oslo, Akershus University Hospital, Lørenskog, Norway
| | - Tone M Tannæs
- Department of Clinical Molecular Biology (Epigen), Akershus University Hospital, Lørenskog, Norway
| | - Ida RK Bukholm
- Department of Gastroenterological Surgery, Akershus University Hospital, Lørenskog, Norway
- Institute of Clinical Medicine, Akershus University Hospital, University of Oslo, Lørenskog, Norway
| | - Geir Bukholm
- Institute of Health and Society, University of Oslo, Oslo, Norway
| |
Collapse
|
27
|
Effect of Host Genotype on Symbiont Titer in the Aphid-Buchnera Symbiosis. INSECTS 2011; 2:423-34. [PMID: 26467737 PMCID: PMC4553553 DOI: 10.3390/insects2030423] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/03/2011] [Revised: 08/23/2011] [Accepted: 09/07/2011] [Indexed: 11/30/2022]
Abstract
Obligate nutritional symbioses require balance between the energetic needs of the host and the symbiont. The resident symbiont population size within a host may have major impacts on host fitness, as both host and symbiont consume and supply metabolites in a shared metabolite pool. Given the massive genome degradation that is a hallmark of bacterial endosymbionts of insects, it is unclear at what level these populations are regulated, and how regulation varies among hosts within natural populations. We measured the titer of the endosymbiont Buchnera aphidicola from different clones of the pea aphid, Acyrthosiphon pisum, and found significant variation in titer, measured as Buchnera genomes per aphid genome, among aphid clones. Additionally, we found that titer can change with the age of the host, and that the number of bacteriocytes within an aphid is one factor likely controlling Buchnera titer. Buchnera titer measurements in clones from a sexual cross indicate that the symbiont genotype is not responsible for variation in titer and that this phenotype is likely non-heritable across sexual reproduction. Symbiont titer is more variable among lab-produced F1 aphid clones than among field-collected ones, suggesting that intermediate titer is favored in natural populations. Potentially, a low heritability of titer during the sexual phase may generate clones with extreme and maladaptive titers each season.
Collapse
|
28
|
Sharma V, Firth AE, Antonov I, Fayet O, Atkins JF, Borodovsky M, Baranov PV. A pilot study of bacterial genes with disrupted ORFs reveals a surprising profusion of protein sequence recoding mediated by ribosomal frameshifting and transcriptional realignment. Mol Biol Evol 2011; 28:3195-211. [PMID: 21673094 DOI: 10.1093/molbev/msr155] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Bacterial genome annotations contain a number of coding sequences (CDSs) that, in spite of reading frame disruptions, encode a single continuous polypeptide. Such disruptions have different origins: sequencing errors, frameshift, or stop codon mutations, as well as instances of utilization of nontriplet decoding. We have extracted over 1,000 CDSs with annotated disruptions and found that about 75% of them can be clustered into 64 groups based on sequence similarity. Analysis of the clusters revealed deep phylogenetic conservation of open reading frame organization as well as the presence of conserved sequence patterns that indicate likely utilization of the nonstandard decoding mechanisms: programmed ribosomal frameshifting (PRF) and programmed transcriptional realignment (PTR). Further enrichment of these clusters with additional homologous nucleotide sequences revealed over 6,000 candidate genes utilizing PRF or PTR. Analysis of the patterns of conservation apparently associated with nontriplet decoding revealed the presence of both previously characterized frameshift-prone sequences and a few novel ones. Since the starting point of our analysis was a set of genes with already annotated disruptions, it is highly plausible that in this study, we have identified only a fraction of all bacterial genes that utilize PRF or PTR. In addition to the identification of a large number of recoded genes, a surprising observation is that nearly half of them are expressed via PTR-a mechanism that, in contrast to PRF, has not yet received substantial attention.
Collapse
Affiliation(s)
- Virag Sharma
- Department of Biochemistry, University College Cork, Cork, Ireland
| | | | | | | | | | | | | |
Collapse
|
29
|
Williams LE, Wernegreen JJ. Unprecedented loss of ammonia assimilation capability in a urease-encoding bacterial mutualist. BMC Genomics 2010; 11:687. [PMID: 21126349 PMCID: PMC3017870 DOI: 10.1186/1471-2164-11-687] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2010] [Accepted: 12/02/2010] [Indexed: 11/15/2022] Open
Abstract
Background Blochmannia are obligately intracellular bacterial mutualists of ants of the tribe Camponotini. Blochmannia perform key nutritional functions for the host, including synthesis of several essential amino acids. We used Illumina technology to sequence the genome of Blochmannia associated with Camponotus vafer. Results Although Blochmannia vafer retains many nutritional functions, it is missing glutamine synthetase (glnA), a component of the nitrogen recycling pathway encoded by the previously sequenced B. floridanus and B. pennsylvanicus. With the exception of Ureaplasma, B. vafer is the only sequenced bacterium to date that encodes urease but lacks the ability to assimilate ammonia into glutamine or glutamate. Loss of glnA occurred in a deletion hotspot near the putative replication origin. Overall, compared to the likely gene set of their common ancestor, 31 genes are missing or eroded in B. vafer, compared to 28 in B. floridanus and four in B. pennsylvanicus. Three genes (queA, visC and yggS) show convergent loss or erosion, suggesting relaxed selection for their functions. Eight B. vafer genes contain frameshifts in homopolymeric tracts that may be corrected by transcriptional slippage. Two of these encode DNA replication proteins: dnaX, which we infer is also frameshifted in B. floridanus, and dnaG. Conclusions Comparing the B. vafer genome with B. pennsylvanicus and B. floridanus refines the core genes shared within the mutualist group, thereby clarifying functions required across ant host species. This third genome also allows us to track gene loss and erosion in a phylogenetic context to more fully understand processes of genome reduction.
Collapse
Affiliation(s)
- Laura E Williams
- The Institute for Genome Sciences and Policy, Duke University, Durham, NC, USA
| | | |
Collapse
|
30
|
Vakhrusheva AA, Kazanov MD, Mironov AA, Bazykin GA. Evolution of prokaryotic genes by shift of stop codons. J Mol Evol 2010; 72:138-46. [PMID: 21082168 DOI: 10.1007/s00239-010-9408-1] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2010] [Accepted: 10/29/2010] [Indexed: 11/30/2022]
Abstract
De novo origin of coding sequence remains an obscure issue in molecular evolution. One of the possible paths for addition (subtraction) of DNA segments to (from) a gene is stop codon shift. Single nucleotide substitutions can destroy the existing stop codon, leading to uninterrupted translation up to the next stop codon in the gene's reading frame, or create a premature stop codon via a nonsense mutation. Furthermore, short indels-caused frameshifts near gene's end may lead to premature stop codons or to translation past the existing stop codon. Here, we describe the evolution of the length of coding sequence of prokaryotic genes by change of positions of stop codons. We observed cases of addition of regions of 3'UTR to genes due to mutations at the existing stop codon, and cases of subtraction of C-terminal coding segments due to nonsense mutations upstream of the stop codon. Many of the observed stop codon shifts cannot be attributed to sequencing errors or rare deleterious variants segregating within bacterial populations. The additions of regions of 3'UTR tend to occur in those genes in which they are facilitated by nearby downstream in-frame triplets which may serve as new stop codons. Conversely, subtractions of coding sequence often give rise to in-frame stop codons located nearby. The amino acid composition of the added region is significantly biased, compared to the overall amino acid composition of the genes. Our results show that in prokaryotes, shift of stop codon is an underappreciated contributor to functional evolution of gene length.
Collapse
Affiliation(s)
- Anna A Vakhrusheva
- Department of Bioengineering and Bioinformatics, M.V. Lomonosov Moscow State University, Vorbyevy Gory 1-73, Moscow 119992, Russia
| | | | | | | |
Collapse
|
31
|
Tse H, Cai JJ, Tsoi HW, Lam EP, Yuen KY. Natural selection retains overrepresented out-of-frame stop codons against frameshift peptides in prokaryotes. BMC Genomics 2010; 11:491. [PMID: 20828396 PMCID: PMC2996987 DOI: 10.1186/1471-2164-11-491] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2010] [Accepted: 09/09/2010] [Indexed: 12/03/2022] Open
Abstract
Background Out-of-frame stop codons (OSCs) occur naturally in coding sequences of all organisms, providing a mechanism of early termination of translation in incorrect reading frame so that the metabolic cost associated with frameshift events can be reduced. Given such a functional significance, we expect statistically overrepresented OSCs in coding sequences as a result of a widespread selection. Accordingly, we examined available prokaryotic genomes to look for evidence of this selection. Results The complete genome sequences of 990 prokaryotes were obtained from NCBI GenBank. We found that low G+C content coding sequences contain significantly more OSCs and G+C content at specific codon positions were the principal determinants of OSC usage bias in the different reading frames. To investigate if there is overrepresentation of OSCs, we modeled the trinucleotide and hexanucleotide biases of the coding sequences using Markov models, and calculated the expected OSC frequencies for each organism using a Monte Carlo approach. More than 93% of 342 phylogenetically representative prokaryotic genomes contain excess OSCs. Interestingly the degree of OSC overrepresentation correlates positively with G+C content, which may represent a compensatory mechanism for the negative correlation of OSC frequency with G+C content. We extended the analysis using additional compositional bias models and showed that lower-order bias like codon usage and dipeptide bias could not explain the OSC overrepresentation. The degree of OSC overrepresentation was found to correlate negatively with the optimal growth temperature of the organism after correcting for the G+C% and AT skew of the coding sequence. Conclusions The present study uses approaches with statistical rigor to show that OSC overrepresentation is a widespread phenomenon among prokaryotes. Our results support the hypothesis that OSCs carry functional significance and have been selected in the course of genome evolution to act against unintended frameshift occurrences. Some results also hint that OSC overrepresentation being a compensatory mechanism to make up for the decrease in OSCs in high G+C organisms, thus revealing the interplay between two different determinants of OSC frequency.
Collapse
Affiliation(s)
- Herman Tse
- Carol Yu Centre for Infection, Department of Microbiology, The University of Hong Kong, Hong Kong, China
| | | | | | | | | |
Collapse
|