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Conservation and Diversification of tRNA t6A-Modifying Enzymes across the Three Domains of Life. Int J Mol Sci 2022; 23:ijms232113600. [PMID: 36362385 PMCID: PMC9654439 DOI: 10.3390/ijms232113600] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2022] [Revised: 10/28/2022] [Accepted: 11/04/2022] [Indexed: 11/09/2022] Open
Abstract
The universal N6-threonylcarbamoyladenosine (t6A) modification occurs at position 37 of tRNAs that decipher codons starting with adenosine. Mechanistically, t6A stabilizes structural configurations of the anticodon stem loop, promotes anticodon–codon pairing and safeguards the translational fidelity. The biosynthesis of tRNA t6A is co-catalyzed by two universally conserved protein families of TsaC/Sua5 (COG0009) and TsaD/Kae1/Qri7 (COG0533). Enzymatically, TsaC/Sua5 protein utilizes the substrates of L-threonine, HCO3−/CO2 and ATP to synthesize an intermediate L-threonylcarbamoyladenylate, of which the threonylcarbamoyl-moiety is subsequently transferred onto the A37 of substrate tRNAs by the TsaD–TsaB –TsaE complex in bacteria or by the KEOPS complex in archaea and eukaryotic cytoplasm, whereas Qri7/OSGEPL1 protein functions on its own in mitochondria. Depletion of tRNA t6A interferes with protein homeostasis and gravely affects the life of unicellular organisms and the fitness of higher eukaryotes. Pathogenic mutations of YRDC, OSGEPL1 and KEOPS are implicated in a number of human mitochondrial and neurological diseases, including autosomal recessive Galloway–Mowat syndrome. The molecular mechanisms underscoring both the biosynthesis and cellular roles of tRNA t6A are presently not well elucidated. This review summarizes current mechanistic understandings of the catalysis, regulation and disease implications of tRNA t6A-biosynthetic machineries of three kingdoms of life, with a special focus on delineating the structure–function relationship from perspectives of conservation and diversity.
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Luthra A, Paranagama N, Swinehart W, Bayooz S, Phan P, Quach V, Schiffer JM, Stec B, Iwata-Reuyl D, Swairjo MA. Conformational communication mediates the reset step in t6A biosynthesis. Nucleic Acids Res 2020; 47:6551-6567. [PMID: 31114923 PMCID: PMC6614819 DOI: 10.1093/nar/gkz439] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Revised: 05/06/2019] [Accepted: 05/09/2019] [Indexed: 11/16/2022] Open
Abstract
The universally conserved N6-threonylcarbamoyladenosine (t6A) modification of tRNA is essential for translational fidelity. In bacteria, t6A biosynthesis starts with the TsaC/TsaC2-catalyzed synthesis of the intermediate threonylcarbamoyl adenylate (TC–AMP), followed by transfer of the threonylcarbamoyl (TC) moiety to adenine-37 of tRNA by the TC-transfer complex comprised of TsaB, TsaD and TsaE subunits and possessing an ATPase activity required for multi-turnover of the t6A cycle. We report a 2.5-Å crystal structure of the T. maritima TC-transfer complex (TmTsaB2D2E2) bound to Mg2+-ATP in the ATPase site, and substrate analog carboxy-AMP in the TC-transfer site. Site directed mutagenesis results show that residues in the conserved Switch I and Switch II motifs of TsaE mediate the ATP hydrolysis-driven reactivation/reset step of the t6A cycle. Further, SAXS analysis of the TmTsaB2D2-tRNA complex in solution reveals bound tRNA lodged in the TsaE binding cavity, confirming our previous biochemical data. Based on the crystal structure and molecular docking of TC–AMP and adenine-37 in the TC-transfer site, we propose a model for the mechanism of TC transfer by this universal biosynthetic system.
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Affiliation(s)
- Amit Luthra
- Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA
| | - Naduni Paranagama
- Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA
| | - William Swinehart
- Department of Chemistry, Portland State University, PO Box 751, Portland, OR 97207, USA
| | - Susan Bayooz
- Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA
| | - Phuc Phan
- Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA
| | - Vanessa Quach
- Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA
| | - Jamie M Schiffer
- Schrödinger, 10201 Wateridge Cir Suite 220, San Diego, CA 92121, USA
| | - Boguslaw Stec
- Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA
| | - Dirk Iwata-Reuyl
- Department of Chemistry, Portland State University, PO Box 751, Portland, OR 97207, USA
| | - Manal A Swairjo
- Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA.,The Viral Information Institute, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA
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3
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Luthra A, Swinehart W, Bayooz S, Phan P, Stec B, Iwata-Reuyl D, Swairjo MA. Structure and mechanism of a bacterial t6A biosynthesis system. Nucleic Acids Res 2018; 46:1395-1411. [PMID: 29309633 PMCID: PMC5814804 DOI: 10.1093/nar/gkx1300] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2017] [Revised: 12/13/2017] [Accepted: 12/19/2017] [Indexed: 11/12/2022] Open
Abstract
The universal N(6)-threonylcarbamoyladenosine (t6A) modification at position 37 of ANN-decoding tRNAs is central to translational fidelity. In bacteria, t6A biosynthesis is catalyzed by the proteins TsaB, TsaC/TsaC2, TsaD and TsaE. Despite intense research, the molecular mechanisms underlying t6A biosynthesis are poorly understood. Here, we report biochemical and biophysical studies of the t6A biosynthesis system from Thermotoga maritima. Small angle X-ray scattering analysis reveals a symmetric 2:2 stoichiometric complex of TsaB and TsaD (TsaB2D2), as well as 2:2:2 complex (TsaB2D2E2), in which TsaB acts as a dimerization module, similar to the role of Pcc1 in the archaeal system. The TsaB2D2 complex is the minimal platform for the binding of one tRNA molecule, which can then accommodate a single TsaE subunit. Kinetic data demonstrate that TsaB2D2 alone, and a TsaB2D2E1 complex with TsaE mutants deficient in adenosine triphosphatase (ATPase) activity, can catalyze only a single cycle of t6A synthesis, while gel shift experiments provide evidence that the role of TsaE-catalyzed ATP hydrolysis occurs after the release of product tRNA. Based on these results, we propose a model for t6A biosynthesis in bacteria.
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Affiliation(s)
- Amit Luthra
- Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA
| | - William Swinehart
- Department of Chemistry, PO Box 751 Portland State University, Portland, OR 97207, USA
| | - Susan Bayooz
- Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA
| | - Phuc Phan
- Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA
| | - Boguslaw Stec
- Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA
| | - Dirk Iwata-Reuyl
- Department of Chemistry, PO Box 751 Portland State University, Portland, OR 97207, USA
| | - Manal A Swairjo
- Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA
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4
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Thiaville PC, El Yacoubi B, Köhrer C, Thiaville JJ, Deutsch C, Iwata-Reuyl D, Bacusmo JM, Armengaud J, Bessho Y, Wetzel C, Cao X, Limbach PA, RajBhandary UL, de Crécy-Lagard V. Essentiality of threonylcarbamoyladenosine (t(6)A), a universal tRNA modification, in bacteria. Mol Microbiol 2015; 98:1199-221. [PMID: 26337258 DOI: 10.1111/mmi.13209] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/28/2015] [Indexed: 02/06/2023]
Abstract
Threonylcarbamoyladenosine (t(6)A) is a modified nucleoside universally conserved in tRNAs in all three kingdoms of life. The recently discovered genes for t(6)A synthesis, including tsaC and tsaD, are essential in model prokaryotes but not essential in yeast. These genes had been identified as antibacterial targets even before their functions were known. However, the molecular basis for this prokaryotic-specific essentiality has remained a mystery. Here, we show that t(6)A is a strong positive determinant for aminoacylation of tRNA by bacterial-type but not by eukaryotic-type isoleucyl-tRNA synthetases and might also be a determinant for the essential enzyme tRNA(Ile)-lysidine synthetase. We confirm that t(6)A is essential in Escherichia coli and a survey of genome-wide essentiality studies shows that genes for t(6)A synthesis are essential in most prokaryotes. This essentiality phenotype is not universal in Bacteria as t(6)A is dispensable in Deinococcus radiodurans, Thermus thermophilus, Synechocystis PCC6803 and Streptococcus mutans. Proteomic analysis of t(6)A(-) D. radiodurans strains revealed an induction of the proteotoxic stress response and identified genes whose translation is most affected by the absence of t(6)A in tRNAs. Thus, although t(6)A is universally conserved in tRNAs, its role in translation might vary greatly between organisms.
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Affiliation(s)
- Patrick C Thiaville
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL, 32611, USA.,Genetics and Genomics Graduate Program, University of Florida, Gainesville, FL, 32610, USA.,University of Florida Genetics Institute, University of Florida, Gainesville, FL, 32610, USA.,Institut de Génétique et Microbiologie, Université of Paris-Sud, Orsay, France
| | - Basma El Yacoubi
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL, 32611, USA
| | - Caroline Köhrer
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Jennifer J Thiaville
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL, 32611, USA
| | - Chris Deutsch
- Department of Chemistry, Portland State University, Portland, OR, 97297, USA
| | - Dirk Iwata-Reuyl
- Department of Chemistry, Portland State University, Portland, OR, 97297, USA
| | - Jo Marie Bacusmo
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL, 32611, USA
| | - Jean Armengaud
- CEA, DSV, IBiTec-S, SPI, Li2D, Laboratory 'Innovative technologies for Detection and Diagnostics', Bagnols-sur-Cèze, F-30200, France
| | - Yoshitaka Bessho
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo, Hyogo, 679-5148, Japan.,Institute of Physics, Academia Sinica, 128 Sec. 2, Academia Rd., Nankang, Taipei, 11529, Taiwan
| | - Collin Wetzel
- Rieveschl Laboratories for Mass Spectrometry, Department of Chemistry, University of Cincinnati, Cincinnati, Ohio, 45221, USA
| | - Xiaoyu Cao
- Rieveschl Laboratories for Mass Spectrometry, Department of Chemistry, University of Cincinnati, Cincinnati, Ohio, 45221, USA
| | - Patrick A Limbach
- Rieveschl Laboratories for Mass Spectrometry, Department of Chemistry, University of Cincinnati, Cincinnati, Ohio, 45221, USA
| | - Uttam L RajBhandary
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Valérie de Crécy-Lagard
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL, 32611, USA.,University of Florida Genetics Institute, University of Florida, Gainesville, FL, 32610, USA
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Zhang W, Collinet B, Perrochia L, Durand D, van Tilbeurgh H. The ATP-mediated formation of the YgjD-YeaZ-YjeE complex is required for the biosynthesis of tRNA t6A in Escherichia coli. Nucleic Acids Res 2015; 43:1804-17. [PMID: 25578970 PMCID: PMC4330362 DOI: 10.1093/nar/gku1397] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
The essential and universal N6-threonylcarbamoyladenosine (t6A) modification at position 37 of ANN-decoding tRNAs plays a pivotal role in translational fidelity through enhancement of the cognate codon recognition and stabilization of the codon–anticodon interaction. In Escherichia coli, the YgjD (TsaD), YeaZ (TsaB), YjeE (TsaE) and YrdC (TsaC) proteins are necessary and sufficient for the in vitro biosynthesis of t6A, using tRNA, ATP, L-threonine and bicarbonate as substrates. YrdC synthesizes the short-lived L-threonylcarbamoyladenylate (TCA), and YgjD, YeaZ and YjeE cooperate to transfer the L-threonylcarbamoyl-moiety from TCA onto adenosine at position 37 of substrate tRNA. We determined the crystal structure of the heterodimer YgjD–YeaZ at 2.3 Å, revealing the presence of an unexpected molecule of ADP bound at an atypical site situated at the YgjD–YeaZ interface. We further showed that the ATPase activity of YjeE is strongly activated by the YgjD–YeaZ heterodimer. We established by binding experiments and SAXS data analysis that YgjD–YeaZ and YjeE form a compact ternary complex only in presence of ATP. The formation of the ternary YgjD–YeaZ–YjeE complex is required for the in vitro biosynthesis of t6A but not its ATPase activity.
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Affiliation(s)
- Wenhua Zhang
- Institut de Biochimie et Biophysique Moléculaire et Cellulaire, UMR 8619, CNRS, Bâtiment 430, Université de Paris-Sud, 91405 Orsay Cedex, France
| | - Bruno Collinet
- Institut de Biochimie et Biophysique Moléculaire et Cellulaire, UMR 8619, CNRS, Bâtiment 430, Université de Paris-Sud, 91405 Orsay Cedex, France Sorbonne Universités, UPMC Univ Paris 06, UFR 927, Sciences de la vie, F-75005 Paris, France
| | - Ludovic Perrochia
- Institut de Génétique et de Microbiologie, Université Paris-Sud, UMR8621-CNRS, 91405 Orsay, France
| | - Dominique Durand
- Institut de Biochimie et Biophysique Moléculaire et Cellulaire, UMR 8619, CNRS, Bâtiment 430, Université de Paris-Sud, 91405 Orsay Cedex, France
| | - Herman van Tilbeurgh
- Institut de Biochimie et Biophysique Moléculaire et Cellulaire, UMR 8619, CNRS, Bâtiment 430, Université de Paris-Sud, 91405 Orsay Cedex, France
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Saturating mutagenesis of an essential gene: a majority of the Neisseria gonorrhoeae major outer membrane porin (PorB) is mutable. J Bacteriol 2013; 196:540-7. [PMID: 24244002 DOI: 10.1128/jb.01073-13] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The major outer membrane porin (PorB) of Neisseria gonorrhoeae is an essential protein that mediates ion exchange between the organism and its environment and also plays multiple roles in human host pathogenesis. To facilitate structure-function studies of porin's multiple roles, we performed saturating mutagenesis at the porB locus and used deep sequencing to identify essential versus mutable residues. Random mutations in porB were generated in a plasmid vector, and mutant gene pools were transformed into N. gonorrhoeae to select for alleles that maintained bacterial viability. Deep sequencing of the input plasmid pools and the output N. gonorrhoeae genomic DNA pools identified mutations present in each, and the mutations in both pools were compared to determine which changes could be tolerated by the organism. We examined the mutability of 328 amino acids in the mature PorB protein and found that 308 of them were likely to be mutable and that 20 amino acids were likely to be nonmutable. A subset of these predictions was validated experimentally. This approach to identifying essential amino acids in a protein of interest introduces an additional application for next-generation sequencing technology and provides a template for future studies of both porin and other essential bacterial genes.
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Muralla R, Lloyd J, Meinke D. Molecular foundations of reproductive lethality in Arabidopsis thaliana. PLoS One 2011; 6:e28398. [PMID: 22164284 PMCID: PMC3229588 DOI: 10.1371/journal.pone.0028398] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2011] [Accepted: 11/07/2011] [Indexed: 11/23/2022] Open
Abstract
The SeedGenes database (www.seedgenes.org) contains information on more than 400 genes required for embryo development in Arabidopsis. Many of these EMBRYO-DEFECTIVE (EMB) genes encode proteins with an essential function required throughout the life cycle. This raises a fundamental question. Why does elimination of an essential gene in Arabidopsis often result in embryo lethality rather than gametophyte lethality? In other words, how do mutant (emb) gametophytes survive and participate in fertilization when an essential cellular function is disrupted? Furthermore, why do some mutant embryos proceed further in development than others? To address these questions, we first established a curated dataset of genes required for gametophyte development in Arabidopsis based on information extracted from the literature. This provided a basis for comparison with EMB genes obtained from the SeedGenes dataset. We also identified genes that exhibited both embryo and gametophyte defects when disrupted by a loss-of-function mutation. We then evaluated the relationship between mutant phenotype, gene redundancy, mutant allele strength, gene expression pattern, protein function, and intracellular protein localization to determine what factors influence the phenotypes of lethal mutants in Arabidopsis. After removing cases where continued development potentially resulted from gene redundancy or residual function of a weak mutant allele, we identified numerous examples of viable mutant (emb) gametophytes that required further explanation. We propose that the presence of gene products derived from transcription in diploid (heterozygous) sporocytes often enables mutant gametophytes to survive the loss of an essential gene in Arabidopsis. Whether gene disruption results in embryo or gametophyte lethality therefore depends in part on the ability of residual, parental gene products to support gametophyte development. We also highlight here 70 preglobular embryo mutants with a zygotic pattern of inheritance, which provide valuable insights into the maternal-to-zygotic transition in Arabidopsis and the timing of paternal gene activation during embryo development.
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Affiliation(s)
- Rosanna Muralla
- Department of Botany, Oklahoma State University, Stillwater, Oklahoma, United States of America
| | - Johnny Lloyd
- Department of Botany, Oklahoma State University, Stillwater, Oklahoma, United States of America
| | - David Meinke
- Department of Botany, Oklahoma State University, Stillwater, Oklahoma, United States of America
- * E-mail:
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Structural analysis of the essential resuscitation promoting factor YeaZ suggests a mechanism of nucleotide regulation through dimer reorganization. PLoS One 2011; 6:e23245. [PMID: 21858042 PMCID: PMC3157347 DOI: 10.1371/journal.pone.0023245] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2011] [Accepted: 07/11/2011] [Indexed: 11/19/2022] Open
Abstract
Background The yeaZ gene product forms part of the conserved network YjeE/YeaZ/YgjD essential for the survival of many Gram-negative eubacteria. Among other as yet unidentified roles, YeaZ functions as a resuscitation promoting factor required for survival and resuscitation of cells in a viable but non-culturable (VBNC) state. Methodology/Principal Findings In order to investigate in detail the structure/function relationship of this family of proteins we have performed X-ray crystallographic studies of Vibrio parahaemolyticus YeaZ. The YeaZ structure showed that it has a classic actin-like nucleotide-binding fold. Comparisons of this crystal structure to that of available homologues from E. coli, T. maritima and S. typhimurium revealed two distinctly different modes of dimer formation. In one form, prevalent in the absence of nucleotide, the putative nucleotide-binding site is incomplete, lacking a binding pocket for a nucleotide base. In the second form, residues from the second subunit complete the nucleotide-binding site. This suggests that the two dimer architectures observed in the crystal structures correspond to a free and a nucleotide-bound form of YeaZ. A multiple sequence alignment of YeaZ proteins from different bacteria allowed us to identify a large conserved hydrophobic patch on the protein surface that becomes exposed upon nucleotide-driven dimer re-arrangement. We hypothesize that the transition between two dimer architectures represents the transition between the ‘on’ and ‘off’ states of YeaZ. The effect of this transition is to alternately expose and bury a docking site for the partner protein YgjD. Conclusions/Significance This paper provides the first structural insight into the putative mechanism of nucleotide regulation of YeaZ through dimer reorganization. Our analysis suggests that nucleotide binding to YeaZ may act as a regulator or switch that changes YeaZ shape, allowing it to switch partners between YjeE and YgjD.
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Jameson-Lee M, Garduño RA, Hoffman PS. DsbA2 (27 kDa Com1-like protein) of Legionella pneumophila catalyses extracytoplasmic disulphide-bond formation in proteins including the Dot/Icm type IV secretion system. Mol Microbiol 2011; 80:835-52. [PMID: 21375592 DOI: 10.1111/j.1365-2958.2011.07615.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In Gram-negative bacteria, thiol oxidoreductases catalyse the formation of disulphide bonds (DSB) in extracytoplasmic proteins. In this study, we sought to identify DSB-forming proteins required for assembly of macromolecular structures in Legionella pneumophila. Here we describe two DSB-forming proteins, one annotated as dsbA1 and the other annotated as a 27 kDa outer membrane protein similar to Com1 of Coxiella burnetii, which we designate as dsbA2. Both proteins are predicted to be periplasmic, and while dsbA1 mutants were readily isolated and without phenotype, dsbA2 mutants were not obtained. To advance studies of DsbA2, a cis-proline residue at position 198 was replaced with threonine that enables formation of stable disulphide-bond complexes with substrate proteins. Expression of DsbA2 P198T mutant protein from an inducible promoter produced dominant-negative effects on DsbA2 function that resulted in loss of infectivity for amoeba and HeLa cells and loss of Dot/Icm T4SS-mediated contact haemolysis of erythrocytes. Analysis of captured DsbA2 P198T-substrate complexes from L. pneumophila by mass spectrometry identified periplasmic and outer membrane proteins that included components of the Dot/Icm T4SS. More broadly, our studies establish a DSB oxidoreductase function for the Com1 lineage of DsbA2-like proteins which appear to be conserved among those bacteria also expressing T4SS.
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Affiliation(s)
- Max Jameson-Lee
- Department of Medicine, Division of Infectious Diseases and International Health, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
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Abstract
Replicon architecture in bacteria is commonly comprised of one indispensable chromosome and several dispensable plasmids. This view has been enriched by the discovery of additional chromosomes, identified mainly by localization of rRNA and/or tRNA genes, and also by experimental demonstration of their requirement for cell growth. The genome of Rhizobium etli CFN42 is constituted by one chromosome and six large plasmids, ranging in size from 184 to 642 kb. Five of the six plasmids are dispensable for cell viability, but plasmid p42e is unusually stable. One possibility to explain this stability would be that genes on p42e carry out essential functions, thus making it a candidate for a secondary chromosome. To ascertain this, we made an in-depth functional analysis of p42e, employing bioinformatic tools, insertional mutagenesis, and programmed deletions. Nearly 11% of the genes in p42e participate in primary metabolism, involving biosynthetic functions (cobalamin, cardiolipin, cytochrome o, NAD, and thiamine), degradation (asparagine and melibiose), and septum formation (minCDE). Synteny analysis and incompatibility studies revealed highly stable replicons equivalent to p42e in content and gene order in other Rhizobium species. A systematic deletion analysis of p42e allowed the identification of two genes (RHE_PE00001 and RHE_PE00024), encoding, respectively, a hypothetical protein with a probable winged helix-turn-helix motif and a probable two-component sensor histidine kinase/response regulator hybrid protein, which are essential for growth in rich medium. These data support the proposal that p42e and its homologous replicons (pA, pRL11, pRLG202, and pR132502) merit the status of secondary chromosomes.
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11
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Galperin MY, Koonin EV. From complete genome sequence to 'complete' understanding? Trends Biotechnol 2010; 28:398-406. [PMID: 20647113 PMCID: PMC3065831 DOI: 10.1016/j.tibtech.2010.05.006] [Citation(s) in RCA: 119] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2010] [Revised: 05/18/2010] [Accepted: 05/28/2010] [Indexed: 12/29/2022]
Abstract
The rapidly accumulating genome sequence data allow researchers to address fundamental biological questions that were not even asked just a few years ago. A major problem in genomics is the widening gap between the rapid progress in genome sequencing and the comparatively slow progress in the functional characterization of sequenced genomes. Here we discuss two key questions of genome biology: whether we need more genomes, and how deep is our understanding of biology based on genomic analysis. We argue that overly specific annotations of gene functions are often less useful than the more generic, but also more robust, functional assignments based on protein family classification. We also discuss problems in understanding the functions of the remaining 'conserved hypothetical' genes.
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Affiliation(s)
- Michael Y Galperin
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA.
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