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Jin D, Li C, Chen X, Wang Y, Al-Rasheid KAS, Stover NA, Shao C, Zhang T. Decryption of the survival "black box": gene family expansion promotes the encystment in ciliated protists. BMC Genomics 2024; 25:286. [PMID: 38500030 PMCID: PMC10946202 DOI: 10.1186/s12864-024-10207-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2023] [Accepted: 03/11/2024] [Indexed: 03/20/2024] Open
Abstract
BACKGROUND Encystment is an important survival strategy extensively employed by microbial organisms to survive unfavorable conditions. Single-celled ciliated protists (ciliates) are popular model eukaryotes for studying encystment, whereby these cells degenerate their ciliary structures and develop cyst walls, then reverse the process under more favorable conditions. However, to date, the evolutionary basis and mechanism for encystment in ciliates is largely unknown. With the rapid development of high-throughput sequencing technologies, genome sequencing and comparative genomics of ciliates have become effective methods to provide insights into above questions. RESULTS Here, we profiled the MAC genome of Pseudourostyla cristata, a model hypotrich ciliate for encystment studies. Like other hypotrich MAC genomes, the P. cristata MAC genome is extremely fragmented with a single gene on most chromosomes, and encodes introns that are generally small and lack a conserved branch point for pre-mRNA splicing. Gene family expansion analyses indicate that multiple gene families involved in the encystment are expanded during the evolution of P. cristata. Furthermore, genomic comparisons with other five representative hypotrichs indicate that gene families of phosphorelay sensor kinase, which play a role in the two-component signal transduction system that is related to encystment, show significant expansion among all six hypotrichs. Additionally, cyst wall-related chitin synthase genes have experienced structural changes that increase them from single-exon to multi-exon genes during evolution. These genomic features potentially promote the encystment in hypotrichs and enhance their ability to survive in adverse environments during evolution. CONCLUSIONS We systematically investigated the genomic structure of hypotrichs and key evolutionary phenomenon, gene family expansion, for encystment promotion in ciliates. In summary, our results provided insights into the evolutionary mechanism of encystment in ciliates.
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Affiliation(s)
- Didi Jin
- Laboratory of Biodiversity and Evolution of Protozoa in Wetland, College of Life Sciences, Shaanxi Normal University, Xi'an, 710119, China
| | - Chao Li
- Key Laboratory of Evolution & Marine Biodiversity (Ministry of Education), and Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao, 266003, China
| | - Xiao Chen
- Laboratory of Marine Protozoan Biodiversity and Evolution, Marine College, Shandong University, Weihai, 264209, China
- Suzhou Research Institute, Shandong University, Suzhou, 215123, China
| | - Yurui Wang
- Laboratory of Biodiversity and Evolution of Protozoa in Wetland, College of Life Sciences, Shaanxi Normal University, Xi'an, 710119, China
| | - Khaled A S Al-Rasheid
- Zoology Department, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia
| | - Naomi A Stover
- Department of Biology, Bradley University, Peoria, 61625, USA
| | - Chen Shao
- Laboratory of Biodiversity and Evolution of Protozoa in Wetland, College of Life Sciences, Shaanxi Normal University, Xi'an, 710119, China.
| | - Tengteng Zhang
- Laboratory of Biodiversity and Evolution of Protozoa in Wetland, College of Life Sciences, Shaanxi Normal University, Xi'an, 710119, China.
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Gaydukova SA, Moldovan MA, Vallesi A, Heaphy SM, Atkins JF, Gelfand MS, Baranov PV. Nontriplet feature of genetic code in Euplotes ciliates is a result of neutral evolution. Proc Natl Acad Sci U S A 2023; 120:e2221683120. [PMID: 37216548 PMCID: PMC10235951 DOI: 10.1073/pnas.2221683120] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Accepted: 04/12/2023] [Indexed: 05/24/2023] Open
Abstract
The triplet nature of the genetic code is considered a universal feature of known organisms. However, frequent stop codons at internal mRNA positions in Euplotes ciliates ultimately specify ribosomal frameshifting by one or two nucleotides depending on the context, thus posing a nontriplet feature of the genetic code of these organisms. Here, we sequenced transcriptomes of eight Euplotes species and assessed evolutionary patterns arising at frameshift sites. We show that frameshift sites are currently accumulating more rapidly by genetic drift than they are removed by weak selection. The time needed to reach the mutational equilibrium is several times longer than the age of Euplotes and is expected to occur after a several-fold increase in the frequency of frameshift sites. This suggests that Euplotes are at an early stage of the spread of frameshifting in expression of their genome. In addition, we find the net fitness burden of frameshift sites to be noncritical for the survival of Euplotes. Our results suggest that fundamental genome-wide changes such as a violation of the triplet character of genetic code can be introduced and maintained solely by neutral evolution.
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Affiliation(s)
- Sofya A. Gaydukova
- Faculty of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Moscow199911, Russia
| | - Mikhail A. Moldovan
- A. A. Kharkevich Institute for Information Transmission Problems RAS, Moscow127051, Russia
| | - Adriana Vallesi
- Laboratory of Eukaryotic Microbiology and Animal Biology, School of Biosciences and Veterinary Medicine, University of Camerino, Camerino62032, Italy
| | - Stephen M. Heaphy
- School of Biochemistry and Cell Biology, University College Cork, CorkT12 XF62, Ireland
| | - John F. Atkins
- School of Biochemistry and Cell Biology, University College Cork, CorkT12 XF62, Ireland
- Department of Human Genetics, University of Utah, Salt Lake City, UT84112
| | - Mikhail S. Gelfand
- A. A. Kharkevich Institute for Information Transmission Problems RAS, Moscow127051, Russia
| | - Pavel V. Baranov
- School of Biochemistry and Cell Biology, University College Cork, CorkT12 XF62, Ireland
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Pawlak K, Błażej P, Mackiewicz D, Mackiewicz P. The Influence of the Selection at the Amino Acid Level on Synonymous Codon Usage from the Viewpoint of Alternative Genetic Codes. Int J Mol Sci 2023; 24:ijms24021185. [PMID: 36674703 PMCID: PMC9866869 DOI: 10.3390/ijms24021185] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2022] [Revised: 12/19/2022] [Accepted: 12/30/2022] [Indexed: 01/11/2023] Open
Abstract
Synonymous codon usage can be influenced by mutations and/or selection, e.g., for speed of protein translation and correct folding. However, this codon bias can also be affected by a general selection at the amino acid level due to differences in the acceptance of the loss and generation of these codons. To assess the importance of this effect, we constructed a mutation-selection model model, in which we generated almost 90,000 stationary nucleotide distributions produced by mutational processes and applied a selection based on differences in physicochemical properties of amino acids. Under these conditions, we calculated the usage of fourfold degenerated (4FD) codons and compared it with the usage characteristic of the pure mutations. We considered both the standard genetic code (SGC) and alternative genetic codes (AGCs). The analyses showed that a majority of AGCs produced a greater 4FD codon bias than the SGC. The mutations producing more thymine or adenine than guanine and cytosine increased the differences in usage. On the other hand, the mutational pressures generating a lot of cytosine or guanine with a low content of adenine and thymine decreased this bias because the nucleotide content of most 4FD codons stayed in the compositional equilibrium with these pressures. The comparison of the theoretical results with those for real protein coding sequences showed that the influence of selection at the amino acid level on the synonymous codon usage cannot be neglected. The analyses indicate that the effect of amino acid selection cannot be disregarded and that it can interfere with other selection factors influencing codon usage, especially in AT-rich genomes, in which AGCs are usually used.
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Primary Structure and Coding Genes of Two Pheromones from the Antarctic Psychrophilic Ciliate, Euplotes focardii. Microorganisms 2022; 10:microorganisms10061089. [PMID: 35744607 PMCID: PMC9229436 DOI: 10.3390/microorganisms10061089] [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] [Received: 04/19/2022] [Revised: 05/14/2022] [Accepted: 05/23/2022] [Indexed: 02/01/2023] Open
Abstract
In ciliates, diffusible cell type-specific pheromones regulate cell growth and mating phenomena acting competitively in both autocrine and heterologous fashion. In Euplotes species, these signaling molecules are represented by species-specific families of structurally homologous small, disulfide-rich proteins, each specified by one of a series of multiple alleles that are inherited without relationships of dominance at the mat-genetic locus of the germinal micronuclear genome, and expressed as individual gene-sized molecules in the somatic macronuclear genome. Here we report the 85-amino acid sequences and the full-length macronuclear nucleotide coding sequences of two pheromones, designated Ef-1 and Ef-2, isolated from the supernatant of a wild-type strain of a psychrophilic species of Euplotes, E. focardii, endemic to Antarctic coastal waters. An overall comparison of the determined E. focardii pheromone and pheromone-gene structures with their homologs from congeneric species provides an initial picture of how an evolutionary increase in the complexity of these structures accompanies Euplotes speciation.
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Kloetzel JA, Aubusson-Fleury A, Butler MD, Banerjee D, Mozzicafreddo M. Sequence and Properties of Cagein, a Coiled-Coil Scaffold Protein Linking Basal Bodies in the Polykinetids of the Ciliate Euplotes aediculatus. J Eukaryot Microbiol 2021; 68:e12850. [PMID: 33738894 DOI: 10.1111/jeu.12850] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 02/23/2021] [Accepted: 03/10/2021] [Indexed: 11/28/2022]
Abstract
In the hypotrich ciliate Euplotes, many individual basal bodies are grouped together in tightly packed clusters, forming ventral polykinetids. These groups of basal bodies (which produce compound ciliary organelles such as cirri and oral membranelles) are cross-linked into ordered arrays by scaffold structures known as "basal-body cages." The major protein comprising Euplotes cages has been previously identified and termed "cagein." Screening a E. aediculatus cDNA expression library with anti-cagein antisera identified a DNA insert containing most of a putative cagein gene; standard PCR techniques were used to complete the sequence. Probes designed from this gene identified a macronuclear "nanochromosome" of ca. 1.5 kb in Southern blots against whole-cell DNA. The protein derived from this sequence (463 residues) is predicted to be hydrophilic and highly charged; however, the native cage structures are highly resistant to salt/detergent extraction. This insolubility could be explained by the coiled-coil regions predicted to extend over much of the length of the derived cagein polypeptide. One frameshift sequence is found within the gene, as well as a short intron. BLAST searches find many ciliates with evident homologues to cagein within their derived genomic sequences.
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Affiliation(s)
- John A Kloetzel
- Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, Maryland, 21250, USA
| | - Anne Aubusson-Fleury
- Biogenese et Fonction des Structures Centriolaires, I2BC, Université Paris Saclay, Gif sur Yvette, 91190, France
| | - Maurice D Butler
- Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, Maryland, 21250, USA
| | | | - Matteo Mozzicafreddo
- Scuola di Bioscienze e Medicina Veterinaria, Università di Camerino, Camerino, Macerata, 62032, Italy
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6
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Many alternative and theoretical genetic codes are more robust to amino acid replacements than the standard genetic code. J Theor Biol 2019; 464:21-32. [DOI: 10.1016/j.jtbi.2018.12.030] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 12/17/2018] [Accepted: 12/19/2018] [Indexed: 02/07/2023]
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Neeb ZT, Hogan DJ, Katzman S, Zahler AM. Preferential expression of scores of functionally and evolutionarily diverse DNA and RNA-binding proteins during Oxytricha trifallax macronuclear development. PLoS One 2017; 12:e0170870. [PMID: 28207760 PMCID: PMC5312943 DOI: 10.1371/journal.pone.0170870] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2016] [Accepted: 01/11/2017] [Indexed: 12/04/2022] Open
Abstract
During its sexual reproduction, the stichotrichous ciliate Oxytricha trifallax orchestrates a remarkable transformation of one of the newly formed germline micronuclear genomes. Hundreds of thousands of gene pieces are stitched together, excised from chromosomes, and replicated dozens of times to yield a functional somatic macronuclear genome composed of ~16,000 distinct DNA molecules that typically encode a single gene. Little is known about the proteins that carry out this process. We profiled mRNA expression as a function of macronuclear development and identified hundreds of mRNAs preferentially expressed at specific times during the program. We find that a disproportionate number of these mRNAs encode proteins that are involved in DNA and RNA functions. Many mRNAs preferentially expressed during macronuclear development have paralogs that are either expressed constitutively or are expressed at different times during macronuclear development, including many components of the RNA polymerase II machinery and homologous recombination complexes. Hundreds of macronuclear development-specific genes encode proteins that are well-conserved among multicellular eukaryotes, including many with links to germline functions or development. Our work implicates dozens of DNA and RNA-binding proteins with diverse evolutionary trajectories in macronuclear development in O. trifallax. It suggests functional connections between the process of macronuclear development in unicellular ciliates and germline specialization and differentiation in multicellular organisms, and argues that gene duplication is a key source of evolutionary innovation in this process.
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Affiliation(s)
- Zachary T. Neeb
- Department of Molecular, Cell and Developmental Biology and Center for Molecular Biology of RNA, University of California Santa Cruz, Santa Cruz, California, United States of America
| | - Daniel J. Hogan
- Tocagen Inc., San Diego, California, United States of America
- * E-mail: (DJH); (AMZ)
| | - Sol Katzman
- Center for Biomolecular Science and Engineering, University of California Santa Cruz, Santa Cruz, California, United States of America
| | - Alan M. Zahler
- Department of Molecular, Cell and Developmental Biology and Center for Molecular Biology of RNA, University of California Santa Cruz, Santa Cruz, California, United States of America
- * E-mail: (DJH); (AMZ)
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8
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A new integrated symmetrical table for genetic codes. Biosystems 2017; 151:21-26. [DOI: 10.1016/j.biosystems.2016.11.004] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Accepted: 11/17/2016] [Indexed: 11/24/2022]
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9
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Baranov PV, Atkins JF, Yordanova MM. Augmented genetic decoding: global, local and temporal alterations of decoding processes and codon meaning. Nat Rev Genet 2015; 16:517-29. [PMID: 26260261 DOI: 10.1038/nrg3963] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The non-universality of the genetic code is now widely appreciated. Codes differ between organisms, and certain genes are known to alter the decoding rules in a site-specific manner. Recently discovered examples of decoding plasticity are particularly spectacular. These examples include organisms and organelles with disruptions of triplet continuity during the translation of many genes, viruses that alter the entire genetic code of their hosts and organisms that adjust their genetic code in response to changing environments. In this Review, we outline various modes of alternative genetic decoding and expand existing terminology to accommodate recently discovered manifestations of this seemingly sophisticated phenomenon.
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Affiliation(s)
- Pavel V Baranov
- School of Biochemistry and Cell Biology, University College Cork, Ireland
| | - John F Atkins
- 1] School of Biochemistry and Cell Biology, University College Cork, Ireland. [2] Department of Human Genetics, University of Utah, 15 N 2030 E Rm. 7410, Salt Lake City, Utah 84112-5330, USA
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10
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Špaková T, Pristaš P, Javorský P. Telomere repeats and macronuclear DNA organization in the soil ciliate Kahliella matisi (Ciliophora, Hypotricha). Eur J Protistol 2014; 50:231-5. [PMID: 24882684 DOI: 10.1016/j.ejop.2014.03.002] [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: 09/09/2013] [Revised: 02/27/2014] [Accepted: 03/01/2014] [Indexed: 11/29/2022]
Abstract
To better understand the structure of macronuclear chromosomes in ciliates, the organization of macronuclear DNA was investigated in the hypotrich Kahliella matisi. Total DNA of K. matisi separated by agarose gel electrophoresis showed continuous smear ranging in size from ∼500bp to ∼15kb. This fragmentation was found to be due to the presence of gene-sized macronuclear chromosomes. The sequence analysis of four randomly cloned macronuclear chromosomes showed that K. matisi telomeres consist of 5'-dC4A4-3' repeats and carry one or two open reading frames. The transcription unit was found to be flanked with non-coding AT rich 5' leader and 3' trailer. No consensus transcription-regulatory sequences were identified in 5' leader and only one of analyzed gene-sized chromosomes showed the presence of conserved poly(A) addition signal sequence in 3' trailer. All ORFs showed highest relatedness to Oxytricha trifallax macronuclear chromosomes with conserved exon/intron structure. Sequence comparisons indicate that macronuclear chromosome organization is at least partially conserved in ciliates.
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Affiliation(s)
- Tímea Špaková
- Associated Tissue Bank of Faculty of Medicine of P. J. Šafárik University and L. Pasteur University Hospital, Trieda SNP 1, 041 66 Košice, Slovakia.
| | - Peter Pristaš
- Institute of Animal Physiology, Slovak Academy of Sciences, Šoltésovej 4-6, 040 01 Košice, Slovakia
| | - Peter Javorský
- Institute of Animal Physiology, Slovak Academy of Sciences, Šoltésovej 4-6, 040 01 Košice, Slovakia
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11
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Yang G, Yang G, Aprile L, Turturo V, Pucciarelli S, Pucciarelli S, Miceli C. Characterization and comparative analysis of psychrophilic and mesophilic alpha-amylases from Euplotes species: a contribution to the understanding of enzyme thermal adaptation. Biochem Biophys Res Commun 2013; 438:715-20. [PMID: 23916704 DOI: 10.1016/j.bbrc.2013.07.113] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Accepted: 07/28/2013] [Indexed: 10/26/2022]
Abstract
The eukaryotic α-amylase isolated from the psychrophilic ciliated protozoon Euplotes focardii (EfAmy) was expressed in Escherichia coli and biochemically characterized. Its enzymatic activity was compared to that of the homologous protein from the mesophilic congeneric species Euplotes crassus (EcAmy). The comparison of the amino acid composition and the surface residue composition of the two enzymes indicated a preference for tiny residues and the avoidance of charged, aromatic and hydrophobic residues in EfAmy. Our comparative homology modeling study reveals a lack of surface salt bridges, a decreased number of the surface charged residues, decreased hydrogen bonds and bound ions, and a reduction of aromatic-sulfur interactions, cationic-π interactions and disulfide interactions in EfAmy. In contrast, sequence alignment and homology modeling showed five unconserved prolines located on the surface loops of EcAmy. By analyzing amylolytic activity towards soluble starch as the substrate, we determined the temperature and pH dependence, thermostability and kinetic parameters of these two enzymes. We demonstrated that EfAmy shows the characteristics of a psychrophilic α-amylase, such as the highest hydrolytic activity at low temperatures and high thermolability. In contrast, the EcAmy showed mesophilic characteristics with the highest activity at moderate temperatures and a more than 2-fold increased half-life at 50°C compared to EfAmy. The kcat and KM values of EfAmy were higher than those of the mesophilic EcAmy at all tested temperatures. Furthermore, both EfAmy and EcAmy showed maximum activities at pH 9 and maintained high activities in the presence of surfactants. These results suggest the potential applications of EfAmy and EcAmy as ingredients in detergents for industrial applications.
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Affiliation(s)
- Guang Yang
- School of Biosciences and Biotechnology, University of Camerino, Camerino, MC, Italy
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12
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Yang G, De Santi C, de Pascale D, Pucciarelli S, Pucciarelli S, Miceli C. Characterization of the first eukaryotic cold-adapted patatin-like phospholipase from the psychrophilic Euplotes focardii: Identification of putative determinants of thermal-adaptation by comparison with the homologous protein from the mesophilic Euplotes crassus. Biochimie 2013; 95:1795-806. [PMID: 23796575 DOI: 10.1016/j.biochi.2013.06.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2012] [Accepted: 06/13/2013] [Indexed: 11/28/2022]
Abstract
The ciliated protozoon Euplotes focardii, originally isolated from the coastal seawaters of Terra Nova Bay in Antarctica, shows a strictly psychrophilic phenotype, including optimal survival and multiplication rates at 4-5 °C. This characteristic makes E. focardii an ideal model species for identifying the molecular bases of cold adaptation in psychrophilic organisms, as well as a suitable source of novel cold-active enzymes for industrial applications. In the current study, we characterized the patatin-like phospholipase from E. focardii (EfPLP), and its enzymatic activity was compared to that of the homologous protein from the mesophilic congeneric species Euplotes crassus (EcPLP). Both EfPLP and EcPLP have consensus motifs conserved in other patatin-like phospholipases. By analyzing both esterase and phospholipase A2 activity, we determined the thermostability and the optimal pH, temperature dependence and substrates of these enzymes. We demonstrated that EfPLP shows the characteristics of a psychrophilic phospholipase. Furthermore, we analyzed the enzymatic activity of three engineered versions of the EfPLP, in which unique residues of EfPLP, Gly80, Ala201 and Val204, were substituted through site-directed mutagenesis with residues found in the E. crassus homolog (Glu, Pro and Ile, respectively). Additionally, three corresponding mutants of EcPLP were also generated and characterized. These analyses showed that the substitution of amino acids with rigid and bulky charged/hydrophobic side chain in the psychrophilic EfPLP confers enzymatic properties similar to those of the mesophilic patatin-like phospholipase, and vice versa. This is the first report on the isolation and characterization of a cold-adapted patatin-like phospholipase from eukaryotes. The results reported in this paper support the idea that enzyme thermal-adaptation is based mainly on some amino acid residues that influence the structural flexibility of polypeptides and that EfPLP is an attractive biocatalyst for industrial processes at low temperatures.
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Affiliation(s)
- Guang Yang
- School of Biosciences and Biotechnology, University of Camerino, Italy
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13
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Michel CJ, Pirillo G. A permuted set of a trinucleotide circular code coding the 20 amino acids in variant nuclear codes. J Theor Biol 2013. [DOI: 10.1016/j.jtbi.2012.11.023] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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14
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Swart EC, Bracht JR, Magrini V, Minx P, Chen X, Zhou Y, Khurana JS, Goldman AD, Nowacki M, Schotanus K, Jung S, Fulton RS, Ly A, McGrath S, Haub K, Wiggins JL, Storton D, Matese JC, Parsons L, Chang WJ, Bowen MS, Stover NA, Jones TA, Eddy SR, Herrick GA, Doak TG, Wilson RK, Mardis ER, Landweber LF. The Oxytricha trifallax macronuclear genome: a complex eukaryotic genome with 16,000 tiny chromosomes. PLoS Biol 2013; 11:e1001473. [PMID: 23382650 PMCID: PMC3558436 DOI: 10.1371/journal.pbio.1001473] [Citation(s) in RCA: 157] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2012] [Accepted: 12/12/2012] [Indexed: 01/03/2023] Open
Abstract
With more chromosomes than any other sequenced genome, the macronuclear genome of Oxytricha trifallax has a unique and complex architecture, including alternative fragmentation and predominantly single-gene chromosomes. The macronuclear genome of the ciliate Oxytricha trifallax displays an extreme and unique eukaryotic genome architecture with extensive genomic variation. During sexual genome development, the expressed, somatic macronuclear genome is whittled down to the genic portion of a small fraction (∼5%) of its precursor “silent” germline micronuclear genome by a process of “unscrambling” and fragmentation. The tiny macronuclear “nanochromosomes” typically encode single, protein-coding genes (a small portion, 10%, encode 2–8 genes), have minimal noncoding regions, and are differentially amplified to an average of ∼2,000 copies. We report the high-quality genome assembly of ∼16,000 complete nanochromosomes (∼50 Mb haploid genome size) that vary from 469 bp to 66 kb long (mean ∼3.2 kb) and encode ∼18,500 genes. Alternative DNA fragmentation processes ∼10% of the nanochromosomes into multiple isoforms that usually encode complete genes. Nucleotide diversity in the macronucleus is very high (SNP heterozygosity is ∼4.0%), suggesting that Oxytricha trifallax may have one of the largest known effective population sizes of eukaryotes. Comparison to other ciliates with nonscrambled genomes and long macronuclear chromosomes (on the order of 100 kb) suggests several candidate proteins that could be involved in genome rearrangement, including domesticated MULE and IS1595-like DDE transposases. The assembly of the highly fragmented Oxytricha macronuclear genome is the first completed genome with such an unusual architecture. This genome sequence provides tantalizing glimpses into novel molecular biology and evolution. For example, Oxytricha maintains tens of millions of telomeres per cell and has also evolved an intriguing expansion of telomere end-binding proteins. In conjunction with the micronuclear genome in progress, the O. trifallax macronuclear genome will provide an invaluable resource for investigating programmed genome rearrangements, complementing studies of rearrangements arising during evolution and disease. The macronuclear genome of the ciliate Oxytricha trifallax, contained in its somatic nucleus, has a unique genome architecture. Unlike its diploid germline genome, which is transcriptionally inactive during normal cellular growth, the macronuclear genome is fragmented into at least 16,000 tiny (∼3.2 kb mean length) chromosomes, most of which encode single actively transcribed genes and are differentially amplified to a few thousand copies each. The smallest chromosome is just 469 bp, while the largest is 66 kb and encodes a single enormous protein. We found considerable variation in the genome, including frequent alternative fragmentation patterns, generating chromosome isoforms with shared sequence. We also found limited variation in chromosome amplification levels, though insufficient to explain mRNA transcript level variation. Another remarkable feature of Oxytricha's macronuclear genome is its inordinate fondness for telomeres. In conjunction with its possession of tens of millions of chromosome-ending telomeres per macronucleus, we show that Oxytricha has evolved multiple putative telomere-binding proteins. In addition, we identified two new domesticated transposase-like protein classes that we propose may participate in the process of genome rearrangement. The macronuclear genome now provides a crucial resource for ongoing studies of genome rearrangement processes that use Oxytricha as an experimental or comparative model.
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Affiliation(s)
- Estienne C. Swart
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America
| | - John R. Bracht
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America
| | - Vincent Magrini
- The Genome Institute, Washington University School of Medicine, St. Louis, Missouri, United States of America
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Patrick Minx
- The Genome Institute, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Xiao Chen
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America
| | - Yi Zhou
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America
| | - Jaspreet S. Khurana
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America
| | - Aaron D. Goldman
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America
| | - Mariusz Nowacki
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America
- Institute of Cell Biology, University of Bern, Bern, Switzerland
| | - Klaas Schotanus
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America
| | - Seolkyoung Jung
- Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia, United States of America
| | - Robert S. Fulton
- The Genome Institute, Washington University School of Medicine, St. Louis, Missouri, United States of America
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Amy Ly
- The Genome Institute, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Sean McGrath
- The Genome Institute, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Kevin Haub
- The Genome Institute, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Jessica L. Wiggins
- Sequencing Core Facility, Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey, United States of America
| | - Donna Storton
- Sequencing Core Facility, Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey, United States of America
| | - John C. Matese
- Sequencing Core Facility, Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey, United States of America
| | - Lance Parsons
- Bioinformatics Group, Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey, United States of America
| | - Wei-Jen Chang
- Department of Biology, Hamilton College, Clinton, New York, United States of America
| | - Michael S. Bowen
- Biology Department, Bradley University, Peoria, Illinois, United States of America
| | - Nicholas A. Stover
- Biology Department, Bradley University, Peoria, Illinois, United States of America
| | - Thomas A. Jones
- Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia, United States of America
| | - Sean R. Eddy
- Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia, United States of America
| | - Glenn A. Herrick
- Biology Department, University of Utah, Salt Lake City, Utah, United States of America
| | - Thomas G. Doak
- Department of Biology, University of Indiana, Bloomington, Indiana, United States of America
| | - Richard K. Wilson
- The Genome Institute, Washington University School of Medicine, St. Louis, Missouri, United States of America
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Elaine R. Mardis
- The Genome Institute, Washington University School of Medicine, St. Louis, Missouri, United States of America
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Laura F. Landweber
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America
- * E-mail:
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15
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Chiappori F, Pucciarelli S, Merelli I, Ballarini P, Miceli C, Milanesi L. Structural thermal adaptation of β-tubulins from the Antarctic psychrophilic protozoan Euplotes focardii. Proteins 2012; 80:1154-66. [PMID: 22275059 DOI: 10.1002/prot.24016] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2011] [Revised: 11/17/2011] [Accepted: 12/04/2011] [Indexed: 11/10/2022]
Abstract
Tubulin dimers of psychrophilic eukaryotes can polymerize into microtubules at 4°C, a temperature at which microtubules from mesophiles disassemble. This unique capability requires changes in the primary structure and/or in post-translational modifications of the tubulin subunits. To contribute to the understanding of mechanisms responsible for microtubule cold stability, here we present a computational structural analysis based on molecular dynamics (MD) and experimental data of three β-tubulin isotypes, named EFBT2, EFBT3, and EFBT4, from the Antarctic protozoon Euplotes focardii that optimal temperature for growth and reproduction is 4°C. In comparison to the β-tubulin from E. crassus, a mesophilic Euplotes species, EFBT2, EFBT3, and EFBT4 possess unique amino acid substitutions that confer different flexible properties of the polypeptide, as well as an increased hydrophobicity of the regions involved in microtubule interdimeric contacts that may overcome the microtubule destabilizing effect of cold temperatures. The structural analysis based on MD indicated that all isotypes display different flexibility properties in the regions involved in the formation of longitudinal and lateral contacts during microtubule polymerization. We also investigated the role of E. focardii β-tubulin isotypes during the process of cilia formation. The unique characteristics of the primary and tertiary structures of psychrophilic β-tubulin isotypes seem responsible for the formation of microtubules with distinct dynamic and functional properties.
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Affiliation(s)
- Federica Chiappori
- Istituto di Tecnologie Biomediche-Consiglio Nazionale delle Ricerche, Segrate (MI), Italy.
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16
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Nowacki M, Shetty K, Landweber LF. RNA-Mediated Epigenetic Programming of Genome Rearrangements. Annu Rev Genomics Hum Genet 2011; 12:367-89. [PMID: 21801022 DOI: 10.1146/annurev-genom-082410-101420] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
RNA, normally thought of as a conduit in gene expression, has a novel mode of action in ciliated protozoa. Maternal RNA templates provide both an organizing guide for DNA rearrangements and a template that can transport somatic mutations to the next generation. This opportunity for RNA-mediated genome rearrangement and DNA repair is profound in the ciliate Oxytricha, which deletes 95% of its germline genome during development in a process that severely fragments its chromosomes and then sorts and reorders the hundreds of thousands of pieces remaining. Oxytricha's somatic nuclear genome is therefore an epigenome formed through RNA templates and signals arising from the previous generation. Furthermore, this mechanism of RNA-mediated epigenetic inheritance can function across multiple generations, and the discovery of maternal template RNA molecules has revealed new biological roles for RNA and has hinted at the power of RNA molecules to sculpt genomic information in cells.
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Affiliation(s)
- Mariusz Nowacki
- Institute of Cell Biology, University of Bern, CH-3012 Bern, Switzerland.
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17
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Abstract
Increasing evidence suggests that parentally supplied RNA plays crucial roles during eukaryotic development. This epigenetic contribution may regulate gene expression from the earliest stages. Although present in a variety of eukaryotes, maternally inherited characters are especially prominent in ciliated protozoa, in which parental noncoding RNA molecules instruct whole-genome reorganization. This includes removal of nearly all noncoding DNA and sorting the remaining fragments, producing extremely gene-rich somatic genomes. Chromosome fragmentation and extensive replication produce variable DNA copy numbers in the somatic genome. Understanding the forces that drive and regulate copy number change is fundamental. We show that RNA molecules present in parental cells during sexual reproduction can regulate chromosome copy number in the developing nucleus of the ciliate Oxytricha. Experimentally induced changes in RNA abundance can both increase and decrease the levels of corresponding DNA molecules in progeny, demonstrating epigenetic inheritance of chromosome copy number. These results suggest that maternal RNA, in addition to controlling gene expression or DNA processing, can also program DNA amplification levels.
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18
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Sammet SG, Bastolla U, Porto M. Comparison of translation loads for standard and alternative genetic codes. BMC Evol Biol 2010; 10:178. [PMID: 20546599 PMCID: PMC2909233 DOI: 10.1186/1471-2148-10-178] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2009] [Accepted: 06/14/2010] [Indexed: 11/25/2022] Open
Abstract
Background The (almost) universality of the genetic code is one of the most intriguing properties of cellular life. Nevertheless, several variants of the standard genetic code have been observed, which differ in one or several of 64 codon assignments and occur mainly in mitochondrial genomes and in nuclear genomes of some bacterial and eukaryotic parasites. These variants are usually considered to be the result of non-adaptive evolution. It has been shown that the standard genetic code is preferential to randomly assembled codes for its ability to reduce the effects of errors in protein translation. Results Using a genotype-to-phenotype mapping based on a quantitative model of protein folding, we compare the standard genetic code to seven of its naturally occurring variants with respect to the fitness loss associated to mistranslation and mutation. These fitness losses are computed through computer simulations of protein evolution with mutations that are either neutral or lethal, and different mutation biases, which influence the balance between unfolding and misfolding stability. We show that the alternative codes may produce significantly different mutation and translation loads, particularly for genomes evolving with a rather large mutation bias. Most of the alternative genetic codes are found to be disadvantageous to the standard code, in agreement with the view that the change of genetic code is a mutationally driven event. Nevertheless, one of the studied alternative genetic codes is predicted to be preferable to the standard code for a broad range of mutation biases. Conclusions Our results show that, with one exception, the standard genetic code is generally better able to reduce the translation load than the naturally occurring variants studied here. Besides this exception, some of the other alternative genetic codes are predicted to be better adapted for extreme mutation biases. Hence, the fixation of alternative genetic codes might be a neutral or nearly-neutral event in the majority of the cases, but adaptation cannot be excluded for some of the studied cases.
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Affiliation(s)
- Stefanie Gabriele Sammet
- Institut für Festkörperphysik, Technische Universität Darmstadt, Hochschulstr, 8, 64289 Darmstadt, Germany
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19
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Marziale F, Pucciarelli S, Ballarini P, Melki R, Uzun A, Ilyin VA, Detrich HW, Miceli C. Different roles of two gamma-tubulin isotypes in the cytoskeleton of the Antarctic ciliate Euplotes focardii: remodelling of interaction surfaces may enhance microtubule nucleation at low temperature. FEBS J 2008; 275:5367-82. [PMID: 18959762 DOI: 10.1111/j.1742-4658.2008.06666.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Gamma-tubulin belongs to the tubulin superfamily and plays an essential role in the nucleation of cellular microtubules. In the present study, we report the characterization of gamma-tubulin from the psychrophilic Antarctic ciliate Euplotes focardii. In this organism, gamma-tubulin is encoded by two genes, gamma-T1 and gamma-T2, that produce distinct isotypes. Comparison of the gamma-T1 and gamma-T2 primary sequences to a Euplotesgamma-tubulin consensus, derived from mesophilic (i.e. temperate) congeneric species, revealed the presence of numerous unique amino acid substitutions, particularly in gamma-T2. Structural models of gamma-T1 and gamma-T2, obtained using the 3D structure of human gamma-tubulin as a template, suggest that these substitutions are responsible for conformational and/or polarity differences located: (a) in the regions involved in longitudinal 'plus end' contacts; (b) in the T3 loop that participates in binding GTP; and (c) in the M loop that forms lateral interactions. Relative to gamma-T1, the gamma-T2 gene is amplified by approximately 18-fold in the macronuclear genome and is very strongly transcribed. Using confocal immunofluorescence microscopy, we found that the gamma-tubulins of E. focardii associate throughout the cell cycle with basal bodies of the non-motile dorsal cilia and of all of the cirri of the ventral surface (i.e. adoral membranelles, paraoral membrane, and frontoventral transverse, caudal and marginal cirri). By contrast, only gamma-T2 interacts with the centrosomes of the spindle during micronuclear mitosis. We also established that the gamma-T1 isotype associates only with basal bodies. Our results suggest that gamma-T1 and gamma-T2 perform different functions in the organization of the microtubule cytoskeleton of this protist and are consistent with the hypothesis that gamma-T1 and gamma-T2 have evolved sequence-based structural alterations that facilitate template nucleation of microtubules by the gamma-tubulin ring complex at cold temperatures.
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Affiliation(s)
- Francesca Marziale
- Dipartimento di Biologia Molecolare, Cellulare e Animale, University of Camerino, Italy
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20
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Ricard G, de Graaf RM, Dutilh BE, Duarte I, van Alen TA, van Hoek AH, Boxma B, van der Staay GWM, Moon-van der Staay SY, Chang WJ, Landweber LF, Hackstein JHP, Huynen MA. Macronuclear genome structure of the ciliate Nyctotherus ovalis: single-gene chromosomes and tiny introns. BMC Genomics 2008; 9:587. [PMID: 19061489 PMCID: PMC2633312 DOI: 10.1186/1471-2164-9-587] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2008] [Accepted: 12/05/2008] [Indexed: 01/17/2023] Open
Abstract
BACKGROUND Nyctotherus ovalis is a single-celled eukaryote that has hydrogen-producing mitochondria and lives in the hindgut of cockroaches. Like all members of the ciliate taxon, it has two types of nuclei, a micronucleus and a macronucleus. N. ovalis generates its macronuclear chromosomes by forming polytene chromosomes that subsequently develop into macronuclear chromosomes by DNA elimination and rearrangement. RESULTS We examined the structure of these gene-sized macronuclear chromosomes in N. ovalis. We determined the telomeres, subtelomeric regions, UTRs, coding regions and introns by sequencing a large set of macronuclear DNA sequences (4,242) and cDNAs (5,484) and comparing them with each other. The telomeres consist of repeats CCC(AAAACCCC)n, similar to those in spirotrichous ciliates such as Euplotes, Sterkiella (Oxytricha) and Stylonychia. Per sequenced chromosome we found evidence for either a single protein-coding gene, a single tRNA, or the complete ribosomal RNAs cluster. Hence the chromosomes appear to encode single transcripts. In the short subtelomeric regions we identified a few overrepresented motifs that could be involved in gene regulation, but there is no consensus polyadenylation site. The introns are short (21-29 nucleotides), and a significant fraction (1/3) of the tiny introns is conserved in the distantly related ciliate Paramecium tetraurelia. As has been observed in P. tetraurelia, the N. ovalis introns tend to contain in-frame stop codons or have a length that is not dividable by three. This pattern causes premature termination of mRNA translation in the event of intron retention, and potentially degradation of unspliced mRNAs by the nonsense-mediated mRNA decay pathway. CONCLUSION The combination of short leaders, tiny introns and single genes leads to very minimal macronuclear chromosomes. The smallest we identified contained only 150 nucleotides.
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Affiliation(s)
- Guénola Ricard
- Centre for Molecular and Biomolecular Informatics, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, Geert Nijmegen, the Netherlands.
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21
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22
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McGrath CL, Zufall RA, Katz LA. Variation in macronuclear genome content of three ciliates with extensive chromosomal fragmentation: a preliminary analysis. J Eukaryot Microbiol 2007; 54:242-6. [PMID: 17552979 DOI: 10.1111/j.1550-7408.2007.00257.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The genome architecture of ciliates, including features such as nuclear dualism and large-scale genome rearrangements, impacts gene and genome evolution in these organisms. To better understand the structure of macronuclear chromosomes in ciliates with extensively processed chromosomes, a sample of complete macronuclear chromosomes was sequenced from three ciliate species: Metopus es (Class [Cl]: Armophorea), Nyctotherus ovalis (Cl: Armophorea), and Chilodonella uncinata (Cl: Phyllopharyngea). By cloning whole macronuclear chromosomes into a plasmid vector, we generated nine clones from each of M. es and C. uncinata, and 37 clones from N. ovalis. Analysis of these macronuclear chromosomes provides insight into the evolution of genome features such as chromosome content, gene structure, and genetic code. Phylogenetic patterns can be found in telomere structure and codon usage, which are both more similar in M. es and N. ovalis than C. uncinata. In addition, we provide evidence of lateral transfer of a bacterial endo-beta-mannanase gene onto a M. es chromosome and report the discovery of a 42-bp conserved sequence motif within N. ovalis untranslated regions.
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Affiliation(s)
- Casey L McGrath
- Department of Biological Sciences, Smith College, Northampton, Massachusetts 01063, USA
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23
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Chang WJ, Addis VM, Li AJ, Axelsson E, Ardell DH, Landweber LF. Intron Evolution and Information processing in the DNA polymerase alpha gene in spirotrichous ciliates: a hypothesis for interconversion between DNA and RNA deletion. Biol Direct 2007; 2:6. [PMID: 17270054 PMCID: PMC1805493 DOI: 10.1186/1745-6150-2-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2006] [Accepted: 02/01/2007] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The somatic DNA molecules of spirotrichous ciliates are present as linear chromosomes containing mostly single-gene coding sequences with short 5' and 3' flanking regions. Only a few conserved motifs have been found in the flanking DNA. Motifs that may play roles in promoting and/or regulating transcription have not been consistently detected. Moreover, comparing subtelomeric regions of 1,356 end-sequenced somatic chromosomes failed to identify more putatively conserved motifs. RESULTS We sequenced and compared DNA and RNA versions of the DNA polymerase alpha (pol alpha) gene from nine diverged spirotrichous ciliates. We identified a G-C rich motif aaTACCGC(G/C/T) upstream from transcription start sites in all nine pol alpha orthologs. Furthermore, we consistently found likely polyadenylation signals, similar to the eukaryotic consensus AAUAAA, within 35 nt upstream of the polyadenylation sites. Numbers of introns differed among orthologs, suggesting independent gain or loss of some introns during the evolution of this gene. Finally, we discuss the occurrence of short direct repeats flanking some introns in the DNA pol alpha genes. These introns flanked by direct repeats resemble a class of DNA sequences called internal eliminated sequences (IES) that are deleted from ciliate chromosomes during development. CONCLUSION Our results suggest that conserved motifs are present at both 5' and 3' untranscribed regions of the DNA pol alpha genes in nine spirotrichous ciliates. We also show that several independent gains and losses of introns in the DNA pol alpha genes have occurred in the spirotrichous ciliate lineage. Finally, our statistical results suggest that proven introns might also function in an IES removal pathway. This could strengthen a recent hypothesis that introns evolve into IESs, explaining the scarcity of introns in spirotrichs. Alternatively, the analysis suggests that ciliates might occasionally use intron splicing to correct, at the RNA level, failures in IES excision during developmental DNA elimination.
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Affiliation(s)
- Wei-Jen Chang
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA
- Department of Biology, Hamilton College, Clinton, NY 13323, USA
| | - Victoria M Addis
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA
| | - Anya J Li
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA
| | - Elin Axelsson
- Linnaeus Centre for Bioinformatics, Uppsala University, Box 598, SE 751 24 Uppsala Sweden
| | - David H Ardell
- Linnaeus Centre for Bioinformatics, Uppsala University, Box 598, SE 751 24 Uppsala Sweden
| | - Laura F Landweber
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA
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24
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Skovorodkin I, Pimenov A, Raykhel I, Schimanski B, Ammermann D, Günzl A. alpha-tubulin minichromosome promoters in the stichotrichous ciliate Stylonychia lemnae. EUKARYOTIC CELL 2006; 6:28-36. [PMID: 17085637 PMCID: PMC1800363 DOI: 10.1128/ec.00003-06] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Ciliated protists are model organisms for a number of molecular phenomena including telomerase function, self-splicing introns, and an RNA interference-related mechanism in programmed DNA elimination. Despite this relevance, our knowledge about promoters and transcriptional regulation in these organisms is very limited. The macronuclear genome of stichotrichous ciliates consists of minichromosomes which typically encode a single gene. The 5' nontranscribed spacers are usually no longer than 400 bp and highly suitable for promoter characterizations. We used microinjection of two artificial and differently tagged alpha1 tubulin minichromosomes into the macronucleus of Stylonychia lemnae as a means to characterize in detail the corresponding promoter. Clonal cell lines that stably maintained both minichromosomes were generated, enabling comparative expression analysis by primer extension assays. Deletion and block substitution mutations of one of the minichromosomes revealed a TATA-like element, a putative initiator element, and two distinct upstream sequence elements (USEs). Determination of transcription initiation sites and a sequence alignment indicated that both TATA-like and initiator elements are conserved components of S. lemnae minichromosomes, whereas the USEs appear to be specific for the alpha1 tubulin minichromosome. The alpha2 tubulin minichromosome promoter is very short, comprising the two proximal elements but not the USEs. Despite the latter finding, up-regulation of alpha-tubulin expression in cells treated with concanavalin A activated the alpha2 but not the alpha1 tubulin promoter. These results therefore show that gene expression regulation in S. lemnae occurs at the level of transcription initiation on the basis of structurally different promoters.
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Affiliation(s)
- Ilya Skovorodkin
- Zoologisches Institut der Universität Tübingen, Abteilung Zellbiologie, Auf der Morgenstelle 28, 72076 Tübingen, Germany
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25
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McFarland CP, Chang WJ, Kuo S, Landweber LF. Conserved linkage of two genes on the same macronuclear chromosome in spirotrichous ciliates. Chromosoma 2006; 115:129-38. [PMID: 16520956 DOI: 10.1007/s00412-005-0040-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2005] [Revised: 10/04/2005] [Accepted: 10/05/2005] [Indexed: 11/30/2022]
Abstract
Macronuclear chromosomes of spirotrichous ciliates are mainly "nanochromosomes" containing only a single gene. We identified a two-gene chromosome in the spirotrich Sterkiella histriomuscorum (formerly Oxytricha trifallax) which, unlike other characterized two-gene molecules, contains reading frames oriented tail to tail. These are homologs of ribosomal protein L29 (RPL29) and cyclophilin. We found that both genes are transcribed, with their polyadenylation sites on opposite strands separated by only 135 bp. Furthermore, both genes in S. histriomuscorum are present only on one macronuclear chromosome and do not occur alone or linked to other genes. The corresponding micronuclear locus is fragmented into three nonscrambled gene segments (MDSs), separated by two noncoding segments (IESs). We also found that these two genes are linked on a macronuclear chromosome, similarly arranged tail to tail, in the three spirotrichs Stylonychia lemnae, Uroleptus sp., and Holosticha sp.. In addition, single-gene macronuclear chromosomes containing only the RPL29 gene were detected in the earlier diverged Holosticha and Uroleptus. These observations suggest a possible evolutionary trend towards loss of chromosomal breakage between these two genes. This study is the first to examine gene linkage in the macronucleus of several spirotrichs and may provide insight into the evolution of multi-gene macronuclear chromosomes and chromosomal fragmentation in spirotrichs.
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Affiliation(s)
- Craig P McFarland
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA
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26
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Klobutcher LA. Sequencing of random Euplotes crassus macronuclear genes supports a high frequency of +1 translational frameshifting. EUKARYOTIC CELL 2006; 4:2098-105. [PMID: 16339727 PMCID: PMC1317503 DOI: 10.1128/ec.4.12.2098-2105.2005] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Programmed translational frameshifts have been identified in genes from a broad range of organisms, but typically only a very few genes in a given organism require a frameshift for expression. In contrast, a recent analysis of gene sequences available in GenBank from ciliates in the genus Euplotes indicated that >5% required one or more +1 translational frameshifts to produce their predicted protein products. However, this sample of genes was nonrandom, biased, and derived from multiple Euplotes species. To test whether there truly is an abundance of frameshift genes in Euplotes, and to more accurately assess their frequency, we sequenced a random sample of 25 cloned genes/macronuclear DNA molecules from Euplotes crassus. Three new candidate +1 frameshift genes were identified in the sample that encode a membrane occupation and recognition nexus (MORN) repeat protein, a C(2)H(2)-type zinc finger protein, and a Ser/Thr protein kinase. Reverse transcription-PCR analyses indicate that all three genes are expressed in vegetatively proliferating cells and that the mRNAs retain the requirement of a frameshift. Although the sample of sequenced genes is relatively small, the results indicate that the frequency of genes requiring frameshifts in E. crassus is between 3.7% and 31.7% (at a 95% confidence interval). The current and past data also indicate that frameshift sites are found predominantly in genes that likely encode nonabundant proteins in the cell.
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Affiliation(s)
- Lawrence A Klobutcher
- Department of Molecular, Microbial and Structural Biology, University of Connecticut Health Center, Farmington, CT 06032, USA.
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27
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Lescasse R, Yang T, Grisvard J, Villalobo E, Moch C, Baroin-Tourancheau A, Morin L. Gene structure of the ciliate Sterkiella histriomuscorum based on a combined analysis of DNA and cDNA sequences from 21 macronuclear chromosomes. Chromosoma 2005; 114:344-51. [PMID: 16091962 DOI: 10.1007/s00412-005-0018-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2005] [Revised: 07/01/2005] [Accepted: 07/08/2005] [Indexed: 10/25/2022]
Abstract
Macronuclear deoxyribonucleic acid (DNA) in hypotrichous ciliates consists of a set of linear molecules ranging in size from 0.5 to several tens of kilobases and typically carrying a single gene. Each minichromosome is present at a ploidy of >or=1,000 per macronucleus. These molecules are known as gene-sized molecules. Multigene molecules are also present, but are still poorly described. In analyzing the encystment-excystment cycle of Sterkiella histriomuscorum, we have characterized a set of 21 macronuclear molecules both at the DNA and complementary DNA (cDNA) levels. On a total of 23 validated coding sequences, we mapped the 5' and 3' untranslated regions for a subset of 10 and 18 transcripts, respectively. A combination of DNA and cDNA data allows us to precisely determine several structural features of macronuclear chromosomes, such as the organization of multigene molecules, an intron content higher than expected, and a conserved sequence surrounding the initiation transcription site. It also reveals one coding sequence containing a transcribed 10-bp element that displays the characteristic features of internal eliminated sequences (IES). Its presence in a fraction of the minichromosomes carrying this gene raises the possibility of an incomplete IES excision process during the development of the S. histriomuscorum macronucleus.
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Affiliation(s)
- Rachel Lescasse
- Laboratoire de Biologie Cellulaire 4, UMR CNRS 8080, Evolution et Développement, Université Paris-Sud, Bâtiment 444, 91405, Orsay Cedex, France
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28
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Pucciarelli S, Marziale F, Di Giuseppe G, Barchetta S, Miceli C. Ribosomal cold-adaptation: characterization of the genes encoding the acidic ribosomal P0 and P2 proteins from the Antarctic ciliate Euplotes focardii. Gene 2005; 360:103-10. [PMID: 16143466 DOI: 10.1016/j.gene.2005.06.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2004] [Revised: 04/14/2005] [Accepted: 06/02/2005] [Indexed: 10/25/2022]
Abstract
Molecular adaptation at low temperature requires specificities represented mainly by modifications in the gene sequence and consequently in the protein primary structure. To characterize the molecular mechanisms responsible for ribosome cold-adaptation, we compared the ribosomal P0 and P2 genes from the Antarctic ciliate Euplotes focardii with homologous genes from mesophilic organisms, including the ciliates Tetrahymena thermophila and non cold-adapted Euplotes species. This analysis revealed the presence of non synonymous mutations unique to E. focardii. In the P0 protein the mutations produced amino acid substitutions that increased the molecular flexibility that may facilitate a conformational adjustment associated with the interaction with the GTPase center of the large subunit rRNA, and increased the hydrophobicity of the region involved in the interaction with P1/P2 heterodimer, probably to keep associated the ribosomal stalk in the cold. In the P2 protein the mutations produced amino acid substitutions that increased the N-terminus flexibility, which may facilitate interactions with P1 protein in the formation of the heterodimer, and reduced the mobility of the C-terminus, to stabilize the stalk during ribosomal activity. Finally, P proteins appeared to be valid markers for investigating the phylogenetic origin of early eukaryotes.
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Affiliation(s)
- Sandra Pucciarelli
- Dipartimento di Biologia Molecolare, Cellulare e Animale, University of Camerino, Via F Camerini 2, 62032 Camerino (MC), Italy
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Cavalcanti ARO, Dunn DM, Weiss R, Herrick G, Landweber LF, Doak TG. Sequence features of Oxytricha trifallax (class Spirotrichea) macronuclear telomeric and subtelomeric sequences. Protist 2005; 155:311-22. [PMID: 15552058 DOI: 10.1078/1434461041844196] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
We sequenced and analyzed the subtelomeric regions of 1356 macronuclear "nanochromosomes" of the spirotrichous ciliate Oxytricha trifallax. We show that the telomeres in this species have a length of 20 nt, with minor deviations; there is no correlation between telomere lengths at the two ends of the molecule. A search for open reading frames revealed that the 3' and 5' untranslated regions are short, with a median length of approximately 130 nt, and that surprisingly there are no detectable differences between sequences upstream and downstream of genes. Our results confirm a previously reported purine bias in the first approximately 80 nucleotides of the subtelomeric regions, but with this larger data set we curiously detected a 10 bp periodicity in the bias; we relate this finding to the possible regulatory and structural functions these regions must serve. Palindromic sequences in opposing subtelomeric regions, although present in most sequences, are not statistically significant.
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Affiliation(s)
- Andre R O Cavalcanti
- Department of Ecology and Evolutionary Biology, Princeton University, NJ 08544, USA
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Doak TG, Cavalcanti ARO, Stover NA, Dunn DM, Weiss R, Herrick G, Landweber LF. Sequencing the Oxytricha trifallax macronuclear genome: a pilot project. Trends Genet 2004; 19:603-7. [PMID: 14585610 DOI: 10.1016/j.tig.2003.09.013] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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31
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Doak TG, Witherspoon DJ, Jahn CL, Herrick G. Selection on the genes of Euplotes crassus Tec1 and Tec2 transposons: evolutionary appearance of a programmed frameshift in a Tec2 gene encoding a tyrosine family site-specific recombinase. EUKARYOTIC CELL 2003; 2:95-102. [PMID: 12582126 PMCID: PMC141166 DOI: 10.1128/ec.2.1.95-102.2003] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The Tec1 and Tec2 transposons of the ciliate Euplotes crassus carry a gene for a tyrosine-type site-specific recombinase. The expression of the Tec2 gene apparently uses a programmed +1 frameshift. To test this hypothesis, we first examined whether this gene has evolved under purifying selection in Tec1 and Tec2. Each element carries three genes, and each has evolved under purifying selection for the function of its encoded protein, as evidenced by a dearth of nonsynonymous changes. This distortion of divergence is apparent in codons both 5' and 3' of the frameshift site. Thus, Tec2 transposons have diverged from each other while using a programmed +1 frameshift to produce recombinase, the function of which is under purifying selection. What might this function be? Tyrosine-type site-specific recombinases are extremely rare in eukaryotes, and Tec elements are the first known eukaryotic type II transposons to encode a site-specific recombinase. Tec elements also encode a widespread transposase. The Tec recombinase might function in transposition, resolve products of transposition (bacterial replicative transposons use recombinase or resolvase to separate joined replicons), or provide a function that benefits the ciliate host. Transposons in ciliated protozoa are removed from the macronucleus, and it has been proposed that the transposons provide this "excisase" activity.
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Affiliation(s)
- Thomas G Doak
- Department of Pathology, School of Medicine, University of Utah, Salt Lake City, Utah 84132, USA
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32
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Kloetzel JA, Baroin-Tourancheau A, Miceli C, Barchetta S, Farmar J, Banerjee D, Fleury-Aubusson A. Plateins: a novel family of signal peptide-containing articulins in euplotid ciliates. J Eukaryot Microbiol 2003; 50:19-33. [PMID: 12674476 DOI: 10.1111/j.1550-7408.2003.tb00102.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
In euplotid ciliates, the cortex is reinforced by alveolar plates--proteinaceous scales located within the membranous alveolar sacs, forming a monolayer just below the plasma membrane. This system appears to play a cytoskeletal role analogous to that provided by the fibrous epiplasm found beneath the cortical alveoli in other ciliates. In Euplotes aediculatus, the major alveolar plate proteins (termed alpha-, beta-, and gamma-plateins) have been identified. Using anti-platein antibodies, an expression library of Euplotes genes was screened, and a platein gene identified, cloned, and completely sequenced. Comparison of its derived amino acid sequence with microsequences obtained directly from purified plateins identified this gene as encoding one of the closely related beta- or gamma-plateins. The derived protein, of 644 amino acids (74.9 kDa), is very acidic (pI = 4.88). Microsequences from authentic alpha-platein were then used to design oligonucleotide primers, which yielded, via a PCR-based approach, the sequences of two alpha-platein genes from E. aediculatus. Even more acidic proteins, the derived alpha1- and alpha2-plateins contain 536 and 501 residues, respectively. Analyses of their amino acid sequences revealed the plateins to be members of the articulin superfamily of cytoskeletal proteins, first described in Euglena and now identified in the ciliate Pseudomicrothorax and in Plasmodium. The hallmark articulin repetitive motifs (based on degenerate valine- and proline-rich 12-mers) are present in all three plateins. In beta/gamma-platein this primary motif domain (27 repeats) is central in the molecule, whereas the primary repeats in the alpha-plateins lie near their C-termini. A cluster of proline-rich pentameric secondary repeats is found in the C-terminus of beta/gamma-platein, but near the N-terminus of alpha-plateins. All three plateins contain canonical N-terminal signal sequences, unique among known cytoskeletal proteins. The presence of start-transfer sequences correlates well with the final intra-alveolar location of these proteins. This feature, and significant differences from known articulins in amino acid usage and arrangement within the repeat domains, lead us to propose that the plateins comprise a new family of articulin-related proteins. Efforts to follow microscopically the assembly of plateins into new alveolar plates during pre-fission morphogenesis are underway.
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Affiliation(s)
- John A Kloetzel
- Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, Maryland 21250, USA.
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Ammermann D, Hellmer KH, Zassoukhina I, Skovorodkin I. Response to X-ray- and cis Pt-induced DNA damage in Stylonychia lemnae (Ciliata, Protozoa). Eur J Protistol 2003. [DOI: 10.1078/0932-4739-00911] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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34
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Fetzer CP, Hogan DJ, Lipps HJ. A PIWI homolog is one of the proteins expressed exclusively during macronuclear development in the ciliate Stylonychia lemnae. Nucleic Acids Res 2002; 30:4380-6. [PMID: 12384584 PMCID: PMC137143 DOI: 10.1093/nar/gkf579] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In the course of macronuclear differentiation in spirotrichous ciliates massive DNA reorganization processes take place, which include splicing, cutting, rearranging and eliminating specific DNA sequences. In order to identify genes involved in these processes we took advantage of suppression subtractive hybridization. We have identified three transcripts that are exclusively expressed during macronuclear development in the ciliate Stylonychia lemnae. Two of the three differentially expressed mRNAs we have analyzed encode for novel proteins. One gene, mdp1 [macronuclear development protein 1 (MDP1)], encodes a homolog of the PIWI protein family. PIWI proteins are involved in germline differentiation processes and RNA silencing in worms, flies, mice, humans and in plants. Possible functions of the S.lemnae PIWI related protein MDP1 in the regulation of macronuclear development will be discussed.
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Affiliation(s)
- Christian P Fetzer
- Institute of Cell Biology, University Witten/Herdecke, Stockumer Strasse 10, 58453 Witten, Germany
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35
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Williams KR, Doak TG, Herrick G. Telomere formation on macronuclear chromosomes of Oxytricha trifallax and O. fallax: alternatively processed regions have multiple telomere addition sites. BMC Genet 2002; 3:16. [PMID: 12199911 PMCID: PMC128808 DOI: 10.1186/1471-2156-3-16] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2002] [Accepted: 08/28/2002] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND Ciliates employ massive chromatid breakage and de novo telomere formation during generation of the somatic macronucleus. Positions flanking the 81-MAC locus are reproducibly cut. But those flanking the Common Region are proposed to often escape cutting, generating three nested macronuclear chromosomes, two retaining "arms" still appended to the Common Region. Arm-distal positions must differ (in cis) from the Common Region flanks. RESULTS The Common-Region-flanking positions also differ from the arm-distal positions in that they are "multi-TAS" regions: anchored PCR shows heterogeneous patterns of telomere addition sites, but arm-distal sites do not. The multi-TAS patterns are reproducible, but are sensitive to the sequence of the allele being processed. Thus, random degradation following chromatid cutting does not create this heterogeneity; these telomere addition sites also must be dictated by cis-acting sequences. CONCLUSIONS Most ciliates show such micro-heterogeneity in the precise positions of telomere addition sites. Telomerase is believed to be tightly associated with, and act in concert with, the chromatid-cutting nuclease: heterogeneity must be the result of intervening erosion activity. Our "weak-sites" hypothesis explains the correlation between alternative chromatid cutting at the Common Region boundaries and their multi-TAS character: when the chromatid-breakage machine encounters either a weak binding site or a weak cut site at these regions, then telomerase dissociates prematurely, leaving the new end subject to erosion by an exonuclease, which pauses at cis-acting sequences; telomerase eventually heals these resected termini. Finally, we observe TAS positioning influenced by trans-allelic interactions, reminiscent of transvection.
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Affiliation(s)
- Kevin R Williams
- Department of Pathology, University of Utah School of Medicine, Salt Lake City UT 84132-2501, USA
| | - Thomas G Doak
- Department of Pathology, University of Utah School of Medicine, Salt Lake City UT 84132-2501, USA
| | - Glenn Herrick
- Department of Pathology, University of Utah School of Medicine, Salt Lake City UT 84132-2501, USA
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36
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Callejas S, Gutiérrez JC. A simple and rapid PCR-based method to isolate complete small macronuclear minichromosomes from hypotrich ciliates: 5S rDNA and S26 ribosomal protein gene of Oxytricha (Sterkiella) nova. Protist 2002; 153:133-42. [PMID: 12125755 DOI: 10.1078/1434-4610-00092] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Hypotrich ciliates present a macronuclear genome consisting of gene-sized instead of chromosome-sized DNA molecules. Exploiting this unique eukaryotic genome feature, we introduce, for the first time in ciliates, a rapid and easy PCR method using telomeric primers to isolate small complete macronuclear DNA molecules or minichromosomes. Two presumably abundant macronuclear DNA molecules, containing ribosomal genes, were amplified from the Oxytricha (Sterkiella) nova complete genome after using this method, and then were cloned and sequenced. The 5S rDNA sequence of O. (S.) nova is the third one reported among hypotrich ciliates; its primary and secondary structure is compared with other eukaryotic 5S rRNAs. The ribosomal protein S26 gene is the first one reported among ciliates. This "End-End-PCR" method might be useful to obtain similar gene-sized macronuclear molecules from other hypotrich ciliates, and, therefore, to increase our knowledge on ribosomal genes in these eukaryotic microorganisms.
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Affiliation(s)
- Sergio Callejas
- Departamento de Microbiología-III, Facultad de Biología, Universidad Complutense, Madrid, Spain
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37
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Kelminson K, Hewitt E, Arkind C, Kneeland P, DuBois ML, Prescott DM. Histone H4 genes in some stichotrichous ciliates. Eur J Protistol 2002. [DOI: 10.1078/0932-4739-00877] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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38
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Villalobo E, Morin L, Moch C, Lescasse R, Hanna M, Xiao W, Baroin-Tourancheau A. A homologue of CROC-1 in a ciliated protist (Sterkiella histriomuscorum) testifies to the ancient origin of the ubiquitin-conjugating enzyme variant family. Mol Biol Evol 2002; 19:39-48. [PMID: 11752188 DOI: 10.1093/oxfordjournals.molbev.a003980] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Resting cysts of Sterkiella histriomuscorum (Ciliophora, Oxytrichidae) have been shown to contain messenger RNA, one of which codes for a protein significantly similar to CROC-1. CROC-1 is a human regulatory protein capable of transactivating the promoter of c-fos and belongs to a newly characterized family of ubiquitin-conjugating enzyme (E2) variants (UEV). We have determined the corresponding macronuclear gene sequence, which is the first protistan UEV sequence available. The phylogenetic analysis indicates the deep separation and solid clustering of all the UEV sequences within the E2 tree showing the ancient origin of these regulatory genes and their high structural conservation during evolution. Furthermore, overexpression of the ciliate UEV is able to rescue the Saccharomyces cerevisiae mms2 null mutant from killing by DNA damaging agents, implying that the UEV family proteins are functionally conserved. In S. histriomuscorum, expression of UEV is correlated with the growth of the cells as transcripts are present in excysting and vegetative cells but are rapidly down-regulated during starvation. These data support the high conservation of the UEV family in eukaryotes, and a regulatory role of the gene is discussed in relation to known functions of UEVs. This analysis may promote the search for homologues of other regulatory genes (metazoan regulators of differentiation) in ciliates.
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Affiliation(s)
- Eduardo Villalobo
- Laboratoire de Biologie Cellulaire 4, (UPRES-A 8080), Bâtiment 444, Université Paris-Sud, 91405 Orsay Cedex, France
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39
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Prescott DM, Dizick SJ. A unique pattern of intrastrand anomalies in base composition of the DNA in hypotrichs. Nucleic Acids Res 2000; 28:4679-88. [PMID: 11095678 PMCID: PMC115164 DOI: 10.1093/nar/28.23.4679] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The 50 non-coding bases immediately internal to the telomeric repeats in the two 5' ends of macronuclear DNA molecules of a group of hypotrichous ciliates are anomalous in composition, consisting of 61% purines and 39% pyrimidines, A>T (ratio of 44:32), and G>C (ratio of 17:7). These ratio imbalances violate parity rule 2, according to which A should equal T and G should equal C within a DNA strand and therefore pyrimidines should equal purines. The purine-rich and base ratio imbalances are in marked contrast to the rest of the non-coding parts of the molecules, which have the theoretically expected purine content of 50%, with A = T and G = C. The ORFs contain an average of 52% purines as a result of bias in codon usage. The 50 bases that flank the 5' ends of macronuclear sequences in micronuclear DNA (12 cases) consist of approximately 50% purines. Thus, the 50 bases in the 5' ends of macronuclear sequences in micronuclear DNA are islands of purine richness in which A>T and G>C. These islands may serve as signals for the excision of macronuclear molecules during macronuclear development. We have found no published reports of coding or non-coding native DNA with such anomalous base composition.
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Affiliation(s)
- D M Prescott
- University of Colorado, Department of Molecular, Cellular and Developmental Biology, Boulder, CO 80309-0347, USA.
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40
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Aigner S, Lingner J, Goodrich KJ, Grosshans CA, Shevchenko A, Mann M, Cech TR. Euplotes telomerase contains an La motif protein produced by apparent translational frameshifting. EMBO J 2000; 19:6230-9. [PMID: 11080168 PMCID: PMC305813 DOI: 10.1093/emboj/19.22.6230] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2000] [Revised: 09/19/2000] [Accepted: 09/20/2000] [Indexed: 11/12/2022] Open
Abstract
Telomerase is the ribonucleoprotein enzyme responsible for the replication of chromosome ends in most eukaryotes. In the ciliate Euplotes aediculatus, the protein p43 biochemically co-purifies with active telomerase and appears to be stoichiometric with both the RNA and the catalytic protein subunit of this telomerase complex. Here we describe cloning of the gene for p43 and present evidence that it is an authentic component of the telomerase holoenzyme. Comparison of the nucleotide sequence of the cloned gene with peptide sequences of the protein suggests that production of full-length p43 relies on a programmed ribosomal frameshift, an extremely rare translational mechanism. Anti-p43 antibodies immunodeplete telomerase RNA and telomerase activity from E.aediculatus nuclear extracts, indicating that the vast majority of mature telomerase complexes in the cell are associated with p43. The sequence of p43 reveals similarity to the La autoantigen, an RNA-binding protein involved in maturation of RNA polymerase III transcripts, and recombinant p43 binds telomerase RNA in vitro. By analogy to other La proteins, p43 may function in chaperoning the assembly and/or facilitating nuclear retention of telomerase.
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Affiliation(s)
- S Aigner
- Department of Chemistry and Biochemistry and Howard Hughes Medical Institute, University of Colorado, Boulder, CO 80309-0215, USA
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41
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Identification and molecular characterization of a putative ciliary WD-repeat protein in the ciliate Euplotes octocarinatus. Eur J Protistol 2000. [DOI: 10.1016/s0932-4739(00)80030-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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42
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Seegmiller A, Williams KR, Herrick G. Two two-gene macronuclear chromosomes of the hypotrichous ciliates Oxytricha fallax and O. trifallax generated by alternative processing of the 81 locus. DEVELOPMENTAL GENETICS 2000; 20:348-57. [PMID: 9254909 DOI: 10.1002/(sici)1520-6408(1997)20:4<348::aid-dvg6>3.0.co;2-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
We describe the first know macronuclear chromosomes that carry more than one gene in hypotrichous ciliated protozoa. These 4.9- and 2.8-kbp chromosomes each consist almost exclusively of two protein-coding genes, which are conserved and transcribed. The two chromosomes share a common region that consists of a gene that is a member of the family of mitochondrial solute carrier genes (CR-MSC; [Williams and Herrick (1991): Nucleic Acids Res 19:4717-4724]. Each chromosome also carries another gene appended to its common region: The 4.9-kbp chromosome also carries a gene that encodes a protein that is rich in glutamine and charged amino acids and bears regions of heptad repeats characteristic of coiled-coils. Its function is unknown. The second gene of the 2.8 kbp chromosome is a mitochondrial solute carrier gene (LA-MSC); thus, the 2.8-kbp chromosomes consists of two mitochondrial solute carrier paralogs. Phylogenetic analysis indicates that the two genes were duplicated before ciliates diverged from the main eukaryotic lineage and were subsequently juxtaposed. The CR- and LA-MSC genes are each interrupted by three introns. The introns are not in homologous positions, suggesting that they may have originated from multiple group II intron transpositions. These chromosomes and their genes are encoded in the Oxytricha germline by the 81 locus. This locus is alternatively processed to generate a nested set of three macronuclear chromosomes, the 4.9- and 2.8-kbp chromosomes and a third (1.6 kbp) which consists almost exclusively of the shared common gene, CR-MSC. Such alternative processing is common in macronuclear development of O. fallax [Cartinhour and Herrick (1984): Mol Cell Biol 4:931-938]. Possible functions for alternative processing are considered; e.g., it may serve to physically link genes to allow co-regulation or co-replication by a common cis-acting sequence.
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Affiliation(s)
- A Seegmiller
- Department of Oncological Sciences, University of Utah School of Medicine, Salt Lake City 84132, USA
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43
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Pérez-Romero P, Villalobo E, Díaz-Ramos C, Calvo P, Torres A. Actin of Histriculus cavicola: characteristics of the highly divergent hypotrich ciliate actins. J Eukaryot Microbiol 1999; 46:469-72. [PMID: 10519214 DOI: 10.1111/j.1550-7408.1999.tb06063.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A macronuclear gene-sized molecule carrying an actin gene from the hypotrich ciliate, Histriculus cavicola, was characterized. Southern blot analysis using a coding region probe suggested that actin in H. cavicola is encoded by a single gene. A comparison of the promoter regions indicated that the H. cavicola actin gene has a TATA box in the 5' flanking region in a position identical to those in other oxytrich ciliates. The coding sequence of this gene is not interrupted by any introns, and codes for a protein of 375 amino acid residues. This protein shares a high degree of similarity with other oxytrichid actins, and a relatively low similarity with actins from other eukaryotes. Comparative analyses of sequences indicated that most of the amino acid substitutions in hypotrich actins are found in surface loops, while the core structures are well-conserved. The sites that interact with DNase I and several regions involved in actin-actin contact have diverged considerably in hypotrich actins, while nucleotide-binding sites are the best-conserved interaction motif.
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Affiliation(s)
- P Pérez-Romero
- Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, Spain
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44
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Maercker C, Kortwig H, Lipps HJ. Separation of micronuclear DNA of Stylonychia lemnae by pulsed-field electrophoresis and identification of a DNA molecule with a high copy number. Genome Res 1999; 9:654-61. [PMID: 10413404 PMCID: PMC310795] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
DNA from the hypotrichous ciliatae Stylonychia lemnae was separated by PFGE. In addition to the separation of the macronuclear DNA molecules with a size up to approximately 40 kb, we were able to separate the micronuclear DNA with a size between approximately 90 kb and 2 Mb. One very prominent 90-kb DNA band appeared on the pulsed-field gels. We propose that this 90-kb DNA fragment represents a linear plasmid residing in the micronucleus in a very high copy number. About 10% of the micronuclear DNA consists of the 90-kb DNA molecule. It appears in the micronucleus as well as in the macronuclear anlagen during macronuclear development but not in the mature macronucleus. Thus, the multicopy DNA is eliminated during fragmentation of the macronuclear anlagen DNA in the course of macronuclear development. Therefore, this 90-kb DNA molecule might serve as an excellent tool to study the recognition and elimination of DNA during nuclear differentiation of hypotrichous ciliates.
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Affiliation(s)
- C Maercker
- Institute for Cell Biology, University of Witten/Herdecke, D-58448 Witten, Germany.
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45
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Maercker C, Kortwig H, Lipps HJ. Separation of Micronuclear DNA of Stylonychia lemnae by Pulsed-Field Electrophoresis and Identification of a DNA Molecule with a High Copy Number. Genome Res 1999. [DOI: 10.1101/gr.9.7.654] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
DNA from the hypotrichous ciliatae Stylonychia lemnae was separated by PFGE. In addition to the separation of the macronuclear DNA molecules with a size up to ∼40 kb, we were able to separate the micronuclear DNA with a size between ∼90 kb and 2 Mb. One very prominent 90-kb DNA band appeared on the pulsed-field gels. We propose that this 90-kb DNA fragment represents a linear plasmid residing in the micronucleus in a very high copy number. About 10% of the micronuclear DNA consists of the 90-kb DNA molecule. It appears in the micronucleus as well as in the macronuclear anlagen during macronuclear development but not in the mature macronucleus. Thus, the multicopy DNA is eliminated during fragmentation of the macronuclear anlagen DNA in the course of macronuclear development. Therefore, this 90-kb DNA molecule might serve as an excellent tool to study the recognition and elimination of DNA during nuclear differentiation of hypotrichous ciliates.
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46
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Abstract
Hypotrichs have evolved extraordinary ways of organizing, manipulating, and replicating the DNA in their micronuclear and macronuclear genomes. Short macronuclear DNA molecules containing single genes are created by excision from chromosomes, accompanied by massive elimination of the germline DNA sequences between genes. Germline genes themselves are interrupted by multiple noncoding segments called internal eliminated segments, or IESs, that divide genes into multiple macronuclear-destined segments, or MDSs. The functional significance of this organization is unknown. Over evolutionary time IESs accumulate mutations rapidly, are inserted into or excised from genes, and shift position along DNA molecules. MDSs are ligated to create functional genes when IESs are spliced out of micronuclear DNA during macronuclear development. MDSs in some germline genes are in scrambled disorder and become unscrambled in association with IES elimination. Replication of DNA in the macronucleus is accomplished by organization of replication enzymes and factors into a structure that sweeps through the macronucleus to replicate the many millions of gene-sized DNA molecules. The significance of many of the bizarre DNA phenomena in the evolutionary/functional success of hypotrichs is still unclear.
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Affiliation(s)
- D M Prescott
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder 80309-0347, USA.
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47
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Grimm M, Brünen-Nieweler C, Junker V, Heckmann K, Beier H. The hypotrichous ciliate Euplotes octocarinatus has only one type of tRNACys with GCA anticodon encoded on a single macronuclear DNA molecule. Nucleic Acids Res 1998; 26:4557-65. [PMID: 9753721 PMCID: PMC147889 DOI: 10.1093/nar/26.20.4557] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Deviations from the universal genetic code have evolved independently several times in ciliated protozoa. Thus, in some species UAA and UAG are no longer used as termination codons, but are read as glutamine, whereas in the genus Euplotes , UGA is translated as cysteine. We have investigated the nature of the tRNACys isoacceptor responsible for decoding UGA in Euplotes cells. Southern hybridization analyses indicated that a single DNA molecule of 630 bp encoding tRNACys exists in the macronucleus of Euplotes octocarinatus . Cloning and sequencing of this fragment revealed that it contains only one copy of a tRNACys gene, which codes for a normal tRNACys with GCA anticodon. This is the first report of the characterization of a tRNA gene in any hypotrichous ciliate. It contains putative signals for initiation and termination of transcription by RNA polymerase III and can be transcribed efficiently in vitro in HeLa cell nuclear extract. Intensive studies on the DNA and tRNA level involving PCR analyses have not disclosed the existence of any tRNA Cys isoacceptor with UCA or ICA anticodons. Translation of the UGA codon by tRNA sub GCA sup Cys necessitates a G:A mispairing in the first anticodon position. We discuss a number of aspects which might contribute to the finding that a near-cognate tRNA isoacceptor efficiently translates the UGA stop codon.
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MESH Headings
- Animals
- Anticodon/genetics
- Base Sequence
- Blotting, Southern
- Cell Nucleus/genetics
- Codon, Terminator
- DNA, Protozoan/genetics
- Escherichia coli/genetics
- Euplotes/genetics
- Genes, Protozoan
- Genetic Code
- Genomic Library
- HeLa Cells
- Humans
- Molecular Sequence Data
- RNA Polymerase III/metabolism
- RNA, Protozoan/genetics
- RNA, Transfer, Cys/genetics
- RNA, Transfer, Cys/isolation & purification
- Restriction Mapping
- Reverse Transcriptase Polymerase Chain Reaction
- Sequence Analysis, DNA
- Transcription, Genetic
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Affiliation(s)
- M Grimm
- Institut für Biochemie, Bayerische Julius-Maximilians-Universität, Biozentrum, Am Hubland, D-97074 Würzburg, Germany
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Tebeau CM, Jahn CL. Sequence and transcript analysis of macronuclear histone H2B genes from Euplotes crassus. Gene X 1997; 197:109-13. [PMID: 9332355 DOI: 10.1016/s0378-1119(97)00248-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Two 1.5-kb macronuclear chromosomes bearing histone H2B genes from the ciliated protozoan Euplotes crassus were cloned and sequenced. Although the noncoding sequences on these macronuclear chromosomes are very different, the genes encode an identical 113-aa histone H2B protein that has a shortened N-terminus and a highly conserved C-terminus relative to histone H2B proteins in other organisms. Primer extension was used to determine the transcription start points. Northern analysis shows that the abundance of H2B mRNA changes relative to DNA replication periods during the sexual phase of the life cycle. Analysis of 3' RACE products indicates that the H2B genes are coexpressed.
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Affiliation(s)
- C M Tebeau
- Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, IL 60611, USA
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Seegmiller A, Williams KR, Herrick G. Two two-gene macronuclear chromosomes of the hypotrichous ciliatesOxytricha fallax andO. trifallax generated by alternative processing of the 81 locus. ACTA ACUST UNITED AC 1997. [DOI: 10.1002/(sici)1520-6408(1997)20:4%3c348::aid-dvg6%3e3.0.co;2-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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