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Meyer I, Volk M, Salto I, Moesser T, Chaoprasid P, Herbrüggen AS, Rohde M, Beckstette M, Heroven AK, Dersch P. RNase-mediated reprogramming of Yersinia virulence. PLoS Pathog 2024; 20:e1011965. [PMID: 39159284 PMCID: PMC11361751 DOI: 10.1371/journal.ppat.1011965] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2024] [Revised: 08/29/2024] [Accepted: 07/15/2024] [Indexed: 08/21/2024] Open
Abstract
RNA degradation is an essential process that allows bacteria to regulate gene expression and has emerged as an important mechanism for controlling virulence. However, the individual contributions of RNases in this process are mostly unknown. Here, we tested the influence of 11 potential RNases in the intestinal pathogen Yersinia pseudotuberculosis on the expression of its type III secretion system (T3SS) and associated effectors (Yops) that are encoded on the Yersinia virulence plasmid. We found that exoribonuclease PNPase and endoribonuclease RNase III inhibit T3SS and yop gene transcription by repressing the synthesis of LcrF, the master activator of Yop-T3SS. Loss of both RNases led to an increase in lcrF mRNA levels. Our work indicates that PNPase exerts its influence via YopD, which accelerates lcrF mRNA degradation. Loss of RNase III, on the other hand, results in the downregulation of the CsrB and CsrC RNAs, thereby increasing the availability of active CsrA, which has been shown previously to enhance lcrF mRNA translation and stability. This CsrA-promoted increase of lcrF mRNA translation could be supported by other factors promoting the protein translation efficiency (e.g. IF-3, RimM, RsmG) that were also found to be repressed by RNase III. Transcriptomic profiling further revealed that Ysc-T3SS-mediated Yop secretion leads to global reprogramming of the Yersinia transcriptome with a massive shift of the expression from chromosomal to virulence plasmid-encoded genes. A similar reprogramming was also observed in the RNase III-deficient mutant under non-secretion conditions. Overall, our work revealed a complex control system where RNases orchestrate the expression of the T3SS/Yop machinery on multiple levels to antagonize phagocytic uptake and elimination by innate immune cells.
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Affiliation(s)
- Ines Meyer
- Institute for Infectiology, Center for Molecular Biology of Inflammation (ZMBE), University of Münster, Münster, Germany
| | - Marcel Volk
- Institute for Infectiology, Center for Molecular Biology of Inflammation (ZMBE), University of Münster, Münster, Germany
| | - Ileana Salto
- Institute for Infectiology, Center for Molecular Biology of Inflammation (ZMBE), University of Münster, Münster, Germany
| | - Theresa Moesser
- Institute for Infectiology, Center for Molecular Biology of Inflammation (ZMBE), University of Münster, Münster, Germany
| | - Paweena Chaoprasid
- Institute for Infectiology, Center for Molecular Biology of Inflammation (ZMBE), University of Münster, Münster, Germany
| | - Anne-Sophie Herbrüggen
- Institute for Infectiology, Center for Molecular Biology of Inflammation (ZMBE), University of Münster, Münster, Germany
| | - Manfred Rohde
- Department of Molecular Infection Biology, Helmholtz Centre for Infection Research, Braunschweig, Germany
| | - Michael Beckstette
- Department of Molecular Infection Biology, Helmholtz Centre for Infection Research, Braunschweig, Germany
| | - Ann Kathrin Heroven
- Department of Molecular Infection Biology, Helmholtz Centre for Infection Research, Braunschweig, Germany
| | - Petra Dersch
- Institute for Infectiology, Center for Molecular Biology of Inflammation (ZMBE), University of Münster, Münster, Germany
- German Center for Infection Research (DZIF), Partner site HZI Braunschweig and associated site University of Münster, Münster, Germany
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Apura P, Gonçalves LG, Viegas SC, Arraiano CM. The world of ribonucleases from pseudomonads: a short trip through the main features and singularities. Microb Biotechnol 2021; 14:2316-2333. [PMID: 34427985 PMCID: PMC8601179 DOI: 10.1111/1751-7915.13890] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Accepted: 06/30/2021] [Indexed: 11/27/2022] Open
Abstract
The development of synthetic biology has brought an unprecedented increase in the number molecular tools applicable into a microbial chassis. The exploration of such tools into different bacteria revealed not only the challenges of context dependency of biological functions but also the complexity and diversity of regulatory layers in bacterial cells. Most of the standardized genetic tools and principles/functions have been mostly based on model microorganisms, namely Escherichia coli. In contrast, the non-model pseudomonads lack a deeper understanding of their regulatory layers and have limited molecular tools. They are resistant pathogens and promising alternative bacterial chassis, making them attractive targets for further studies. Ribonucleases (RNases) are key players in the post-transcriptional control of gene expression by degrading or processing the RNA molecules in the cell. These enzymes act according to the cellular requirements and can also be seen as the recyclers of ribonucleotides, allowing a continuous input of these cellular resources. This makes these post-transcriptional regulators perfect candidates to regulate microbial physiology. This review summarizes the current knowledge and unique properties of ribonucleases in the world of pseudomonads, taking into account genomic context analysis, biological function and strategies to use ribonucleases to improve biotechnological processes.
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Affiliation(s)
- Patrícia Apura
- Instituto de Tecnologia Química e Biológica António XavierUniversidade Nova de LisboaAv. da República, EANOeiras2780‐157Portugal
| | - Luis G. Gonçalves
- Instituto de Tecnologia Química e Biológica António XavierUniversidade Nova de LisboaAv. da República, EANOeiras2780‐157Portugal
| | - Sandra C. Viegas
- Instituto de Tecnologia Química e Biológica António XavierUniversidade Nova de LisboaAv. da República, EANOeiras2780‐157Portugal
| | - Cecília M. Arraiano
- Instituto de Tecnologia Química e Biológica António XavierUniversidade Nova de LisboaAv. da República, EANOeiras2780‐157Portugal
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Snow S, Bacon E, Bergeron J, Katzman D, Wilhelm A, Lewis O, Syangtan D, Calkins A, Archambault L, Anacker ML, Schlax PJ. Transcript decay mediated by RNase III in Borrelia burgdorferi. Biochem Biophys Res Commun 2020; 529:386-391. [PMID: 32703440 DOI: 10.1016/j.bbrc.2020.05.201] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Accepted: 05/26/2020] [Indexed: 11/29/2022]
Abstract
The causative agent of Lyme disease, Borrelia burgdorferi, requires shifts in gene expression to undergo its natural enzootic cycle between tick and vertebrate hosts. mRNA decay mechanisms play significant roles in governing gene expression in other bacteria, but are not yet characterized in B. burgdorferi. RNase III is an important enzyme in processing ribosomal RNA, but it also plays a role in mRNA decay in many bacteria. We compared RNA decay profiles and steady-state abundances of transcripts in wild-type Borrelia burgdorferi strain B31 and in an RNase III null (rnc-) mutant. Transcripts encoding RNA polymerase subunits (rpoA and rpoS), ribosomal proteins (rpsD, rpsK, rpsM, rplQ, and rpsO), a nuclease (pnp), a flagellar protein (flaB), and a translational regulator (bpuR) decayed more rapidly in the wild-type strain than in the slow growing rnc- mutant indicating that RNA turnover is mediated by RNase III in the bacterium that causes Lyme disease. Additionally, in wild type bacteria, RNA decay rates of rpoS, rpoN, ospA, ospC, bpuR and dbpA transcripts are only modestly affected by changes in the osmolarity.
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Affiliation(s)
- Santina Snow
- Department of Chemistry and Biochemistry, Bates College, Lewiston, ME, USA
| | - Emily Bacon
- Department of Chemistry and Biochemistry, Bates College, Lewiston, ME, USA
| | - Jennifer Bergeron
- Department of Chemistry and Biochemistry, Bates College, Lewiston, ME, USA
| | - David Katzman
- Department of Chemistry and Biochemistry, Bates College, Lewiston, ME, USA
| | - Amelia Wilhelm
- Department of Chemistry and Biochemistry, Bates College, Lewiston, ME, USA
| | - Owen Lewis
- Department of Chemistry and Biochemistry, Bates College, Lewiston, ME, USA
| | - Deepsing Syangtan
- Department of Chemistry and Biochemistry, Bates College, Lewiston, ME, USA
| | - Andrew Calkins
- Department of Chemistry and Biochemistry, Bates College, Lewiston, ME, USA
| | - Linda Archambault
- Department of Chemistry and Biochemistry, Bates College, Lewiston, ME, USA
| | - Melissa L Anacker
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
| | - Paula Jean Schlax
- Department of Chemistry and Biochemistry, Bates College, Lewiston, ME, USA.
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Briani F, Carzaniga T, Dehò G. Regulation and functions of bacterial PNPase. WILEY INTERDISCIPLINARY REVIEWS-RNA 2016; 7:241-58. [PMID: 26750178 DOI: 10.1002/wrna.1328] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Revised: 11/23/2015] [Accepted: 11/23/2015] [Indexed: 01/29/2023]
Abstract
Polynucleotide phosphorylase (PNPase) is an exoribonuclease that catalyzes the processive phosphorolytic degradation of RNA from the 3'-end. The enzyme catalyzes also the reverse reaction of polymerization of nucleoside diphosphates that has been implicated in the generation of heteropolymeric tails at the RNA 3'-end. The enzyme is widely conserved and plays a major role in RNA decay in both Gram-negative and Gram-positive bacteria. Moreover, it participates in maturation and quality control of stable RNA. PNPase autoregulates its own expression at post-transcriptional level through a complex mechanism that involves the endoribonuclease RNase III and translation control. The activity of PNPase is modulated in an intricate and still unclear manner by interactions with small molecules and recruitment in different multiprotein complexes. Not surprisingly, given the wide spectrum of PNPase substrates, PNPase-defective mutations in different bacterial species have pleiotropic effects and perturb the execution of genetic programs involving drastic changes in global gene expression such as biofilm formation, growth at suboptimal temperatures, and virulence.
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Affiliation(s)
- Federica Briani
- Dipartimento di Bioscienze, Università degli Studi di Milano, Milan, Italy
| | - Thomas Carzaniga
- Dipartimento di Bioscienze, Università degli Studi di Milano, Milan, Italy
| | - Gianni Dehò
- Dipartimento di Bioscienze, Università degli Studi di Milano, Milan, Italy
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RNase III-Independent Autogenous Regulation of Escherichia coli Polynucleotide Phosphorylase via Translational Repression. J Bacteriol 2015; 197:1931-8. [PMID: 25825432 DOI: 10.1128/jb.00105-15] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2015] [Accepted: 03/23/2015] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED The complex posttranscriptional regulation mechanism of the Escherichia coli pnp gene, which encodes the phosphorolytic exoribonuclease polynucleotide phosphorylase (PNPase), involves two endoribonucleases, namely, RNase III and RNase E, and PNPase itself, which thus autoregulates its own expression. The models proposed for pnp autoregulation posit that the target of PNPase is a mature pnp mRNA previously processed at its 5' end by RNase III, rather than the primary pnp transcript (RNase III-dependent models), and that PNPase activity eventually leads to pnp mRNA degradation by RNase E. However, some published data suggest that pnp expression may also be regulated through a PNPase-dependent, RNase III-independent mechanism. To address this issue, we constructed isogenic Δpnp rnc(+) and Δpnp Δrnc strains with a chromosomal pnp-lacZ translational fusion and measured β-galactosidase activity in the absence and presence of PNPase expressed by a plasmid. Our results show that PNPase also regulates its own expression via a reversible RNase III-independent pathway acting upstream from the RNase III-dependent branch. This pathway requires the PNPase RNA binding domains KH and S1 but not its phosphorolytic activity. We suggest that the RNase III-independent autoregulation of PNPase occurs at the level of translational repression, possibly by competition for pnp primary transcript between PNPase and the ribosomal protein S1. IMPORTANCE In Escherichia coli, polynucleotide phosphorylase (PNPase, encoded by pnp) posttranscriptionally regulates its own expression. The two models proposed so far posit a two-step mechanism in which RNase III, by cutting the leader region of the pnp primary transcript, creates the substrate for PNPase regulatory activity, eventually leading to pnp mRNA degradation by RNase E. In this work, we provide evidence supporting an additional pathway for PNPase autogenous regulation in which PNPase acts as a translational repressor independently of RNase III cleavage. Our data make a new contribution to the understanding of the regulatory mechanism of pnp mRNA, a process long since considered a paradigmatic example of posttranscriptional regulation at the level of mRNA stability.
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6
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Stability of the osmoregulated promoter-derived proP mRNA is posttranscriptionally regulated by RNase III in Escherichia coli. J Bacteriol 2015; 197:1297-305. [PMID: 25645556 DOI: 10.1128/jb.02460-14] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
UNLABELLED The enzymatic activity of Escherichia coli endo-RNase III determines the stability of a subgroup of mRNA species, including bdm, betT, and proU, whose protein products are associated with the cellular response to osmotic stress. Here, we report that the stability of proP mRNA, which encodes a transporter of osmoprotectants, is controlled by RNase III in response to osmotic stress. We observed that steady-state levels of proP mRNA and ProP protein are inversely correlated with cellular RNase III activity and, in turn, affect the proline uptake capacity of the cell. In vitro and in vivo analyses of proP mRNA revealed RNase III cleavage sites in a stem-loop within the 5' untranslated region present only in proP mRNA species synthesized from the osmoregulated P1 promoter. Introduction of nucleotide substitutions in the cleavage site identified inhibited the ribonucleolytic activity of RNase III on proP mRNA, increasing the steady-state levels and half-life of the mRNA. In addition, decreased RNase III activity coincided with a significant increase in both the half-life and abundance of proP mRNA under hyperosmotic stress conditions. Analysis of the RNA bound to RNase III via in vivo cross-linking and immunoprecipitation indicated that this phenomenon is related to the decreased RNA binding capacity of RNase III. Our findings suggest the existence of an RNase III-mediated osmoregulatory network that rapidly balances the expression levels of factors associated with the cellular response to osmotic stress in E. coli. IMPORTANCE Our results demonstrate that RNase III activity on proP mRNA degradation is downregulated in Escherichia coli cells under osmotic stress. In addition, we show that the downregulation of RNase III activity is associated with decreased RNA binding capacity of RNase III under hyperosmotic conditions. In particular, our findings demonstrate a link between osmotic stress and RNase III activity, underscoring the growing importance of posttranscriptional regulation in modulating rapid physiological adjustment to environmental changes.
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Gatewood ML, Bralley P, Weil MR, Jones GH. RNA-Seq and RNA immunoprecipitation analyses of the transcriptome of Streptomyces coelicolor identify substrates for RNase III. J Bacteriol 2012; 194:2228-37. [PMID: 22389483 PMCID: PMC3347082 DOI: 10.1128/jb.06541-11] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2011] [Accepted: 02/23/2012] [Indexed: 11/20/2022] Open
Abstract
RNase III is a key enzyme in the pathways of RNA degradation and processing in bacteria and has been suggested as a global regulator of antibiotic production in Streptomyces coelicolor. Using RNA-Seq, we have examined the transcriptomes of S. coelicolor M145 and an RNase III (rnc)-null mutant of that strain. RNA preparations with reduced levels of structural RNAs were prepared by subtractive hybridization prior to RNA-Seq analysis. We initially identified 7,800 transcripts of known and putative protein-coding genes in M145 and the null mutant, JSE1880, along with transcripts of 21 rRNA genes and 65 tRNA genes. Approximately 3,100 of the protein-coding transcripts were categorized as low-abundance transcripts. For further analysis, we selected those transcripts of known and putative protein-coding genes whose levels changed by ≥ 2-fold between the two S. coelicolor strains and organized those transcripts into 16 functional categories. We refined our analysis by performing RNA immunoprecipitation of the mRNA preparation from JSE1880 using a mutant RNase III protein that binds to transcripts but does not cleave them. This analysis identified ca. 800 transcripts that were enriched in the RNA immunoprecipitates, including 28 transcripts whose levels also changed by ≥ 2-fold in the RNA-Seq analysis. We compare our results with those obtained by microarray analysis of the S. coelicolor transcriptome and with studies describing the characterization of small noncoding RNAs. We have also used the RNA immunoprecipitation results to identify new substrates for RNase III cleavage.
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Affiliation(s)
| | | | - M. Ryan Weil
- Emory Genome Center, Emory University, Atlanta, Georgia, USA
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8
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RNase III-dependent expression of the rpsO-pnp operon of Streptomyces coelicolor. J Bacteriol 2011; 193:4371-9. [PMID: 21742867 DOI: 10.1128/jb.00452-11] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have examined the expression of the rpsO-pnp operon in an RNase III (rnc) mutant of Streptomyces coelicolor. Western blotting demonstrated that polynucleotide phosphorylase (PNPase) levels increased in the rnc mutant, JSE1880, compared with the parental strain, M145, and this observation was confirmed by polymerization assays. It was observed that rpsO-pnp mRNA levels increased in the rnc mutant by 1.6- to 4-fold compared with M145. This increase was observed in exponential, transition, and stationary phases, and the levels of the readthrough transcript, initiated upstream of rpsO in the rpsO-pnp operon; the pnp transcript, initiated in the rpsO-pnp intergenic region; and the rpsO transcript all increased. The increased levels of these transcripts in JSE1880 reflected increased chemical half-lives for each of the three. We demonstrated further that overexpression of the rpsO-pnp operon led to significantly higher levels of PNPase activity in JSE1880 compared to M145, reflecting the likelihood that PNPase expression is autoregulated in an RNase III-dependent manner in S. coelicolor. To explore further the increase in the level of the pnp transcript initiated in the intergenic region in JSE1880, we utilized that transcript as a substrate in assays employing purified S. coelicolor RNase III. These assays revealed the presence of hitherto-undiscovered sites of RNase III cleavage of the pnp transcript. The position of those sites was determined by primer extension, and they were shown to be situated in the loops of a stem-loop structure.
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Messenger RNA Turnover Processes in Escherichia coli, Bacillus subtilis, and Emerging Studies in Staphylococcus aureus. Int J Microbiol 2009; 2009:525491. [PMID: 19936110 PMCID: PMC2777011 DOI: 10.1155/2009/525491] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2008] [Accepted: 11/14/2008] [Indexed: 11/17/2022] Open
Abstract
The regulation of mRNA turnover is a recently appreciated phenomenon by which bacteria modulate gene expression. This review outlines the mechanisms by which three major classes of bacterial trans-acting factors, ribonucleases (RNases), RNA binding proteins, and small noncoding RNAs (sRNA), regulate the transcript stability and protein production of target genes. Because the mechanisms of RNA decay and maturation are best characterized in Escherichia coli, the majority of this review will focus on how these factors modulate mRNA stability in this organism. However, we also address the effects of RNases, RNA binding proteins, sRNAs on mRNA turnover, and gene expression in Bacillus subtilis, which has served as a model for studying RNA processing in gram-positive organisms. We conclude by discussing emerging studies on the role modulating mRNA stability has on gene expression in the important human pathogen Staphylococcus aureus.
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Carpousis AJ, Luisi BF, McDowall KJ. Endonucleolytic initiation of mRNA decay in Escherichia coli. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2009; 85:91-135. [PMID: 19215771 DOI: 10.1016/s0079-6603(08)00803-9] [Citation(s) in RCA: 121] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Instability is a fundamental property of mRNA that is necessary for the regulation of gene expression. In E. coli, the turnover of mRNA involves multiple, redundant pathways involving 3'-exoribonucleases, endoribonucleases, and a variety of other enzymes that modify RNA covalently or affect its conformation. Endoribonucleases are thought to initiate or accelerate the process of mRNA degradation. A major endoribonuclease in this process is RNase E, which is a key component of the degradative machinery amongst the Proteobacteria. RNase E is the central element in a multienzyme complex known as the RNA degradosome. Structural and functional data are converging on models for the mechanism of activation and regulation of RNase E and its paralog, RNase G. Here, we discuss current models for mRNA degradation in E. coli and we present current thinking on the structure and function of RNase E based on recent crystal structures of its catalytic core.
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Affiliation(s)
- Agamemnon J Carpousis
- Laboratoire de Microbiologie et Génétique Moléculaires, CNRS et Université Paul Sabatier, 31062 Toulouse, France
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11
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Abstract
This chapter discusses several topics relating to the mechanisms of mRNA decay. These topics include the following: important physical properties of mRNA molecules that can alter their stability; methods for determining mRNA half-lives; the genetics and biochemistry of proteins and enzymes involved in mRNA decay; posttranscriptional modification of mRNAs; the cellular location of the mRNA decay apparatus; regulation of mRNA decay; the relationships among mRNA decay, tRNA maturation, and ribosomal RNA processing; and biochemical models for mRNA decay. Escherichia coli has multiple pathways for ensuring the effective decay of mRNAs and mRNA decay is closely linked to the cell's overall RNA metabolism. Finally, the chapter highlights important unanswered questions regarding both the mechanism and importance of mRNA decay.
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12
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Timmons L, Court DL, Fire A. Ingestion of bacterially expressed dsRNAs can produce specific and potent genetic interference in Caenorhabditis elegans. Gene 2001; 263:103-12. [PMID: 11223248 DOI: 10.1016/s0378-1119(00)00579-5] [Citation(s) in RCA: 1359] [Impact Index Per Article: 56.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Genetic interference mediated by double-stranded RNA (RNAi) has been a valuable tool in the analysis of gene function in Caenorhabditis elegans. Here we report an efficient induction of RNAi using bacteria to deliver double-stranded RNA. This method makes use of bacteria that are deficient in RNaseIII, an enzyme that normally degrades a majority of dsRNAs in the bacterial cell. Bacteria deficient for RNaseIII were engineered to produce high quantities of specific dsRNA segments. When fed to C. elegans, such engineered bacteria were found to produce populations of RNAi-affected animals with phenotypes that were comparable in expressivity to the corresponding loss-of-function mutants. We found the method to be most effective in inducing RNAi for non-neuronal tissue of late larval and adult hermaphrodites, with decreased effectiveness in the nervous system, in early larval stages, and in males. Bacteria-induced RNAi phenotypes could be maintained over the course of several generations with continuous feeding, allowing for convenient assessments of the biological consequences of specific genetic interference and of continuous exposure to dsRNAs.
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Affiliation(s)
- L Timmons
- Department of Embryology, Carnegie Institution of Washington, 115 West University Parkway, Baltimore, MD 21210, USA
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13
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Coburn GA, Mackie GA. Degradation of mRNA in Escherichia coli: an old problem with some new twists. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1999; 62:55-108. [PMID: 9932452 DOI: 10.1016/s0079-6603(08)60505-x] [Citation(s) in RCA: 241] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Metabolic instability is a hallmark property of mRNAs in most if not all organisms and plays an essential role in facilitating rapid responses to regulatory cues. This article provides a critical examination of recent progress in the enzymology of mRNA decay in Escherichia coli, focusing on six major enzymes: RNase III, RNase E, polynucleotide phosphorylase, RNase II, poly(A) polymerase(s), and RNA helicase(s). The first major advance in our thinking about mechanisms of RNA decay has been catalyzed by the possibility that mRNA decay is orchestrated by a multicomponent mRNA-protein complex (the "degradosome"). The ramifications of this discovery are discussed and developed into mRNA decay models that integrate the properties of the ribonucleases and their associated proteins, the role of RNA structure in determining the susceptibility of an RNA to decay, and some of the known kinetic features of mRNA decay. These models propose that mRNA decay is a vectorial process initiated primarily at or near the 5' terminus of susceptible mRNAs and propagated by successive endonucleolytic cleavages catalyzed by RNase E in the degradosome. It seems likely that the degradosome can be tethered to its substrate, either physically or kinetically through a preference for monphosphorylated RNAs, accounting for the usual "all or none" nature of mRNA decay. A second recent advance in our thinking about mRNA decay is the rediscovery of polyadenylated mRNA in bacteria. Models are provided to account for the role of polyadenylation in facilitating the 3' exonucleolytic degradation of structured RNAs. Finally, we have reviewed the documented properties of several well-studied paradigms for mRNA decay in E. coli. We interpret the published data in light of our models and the properties of the degradosome. It seems likely that the study of mRNA decay is about to enter a phase in which research will focus on the structural basis for recognition of cleavage sites, on catalytic mechanisms, and on regulation of mRNA decay.
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Affiliation(s)
- G A Coburn
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, Canada
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14
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Granger LL, O'Hara EB, Wang RF, Meffen FV, Armstrong K, Yancey SD, Babitzke P, Kushner SR. The Escherichia coli mrsC gene is required for cell growth and mRNA decay. J Bacteriol 1998; 180:1920-8. [PMID: 9537393 PMCID: PMC107108 DOI: 10.1128/jb.180.7.1920-1928.1998] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
We have identified a gene in Escherichia coli that is required for both the normal decay of mRNA and RNA synthesis. Originally designated mrsC (mRNA stability), the mrsC505 mutation described here is, in fact, an allele of the hflB/ftsH locus (R.-F. Wang et al., J. Bacteriol. 180:1929-1938, 1998). Strains carrying the thermosensitive mrsC505 allele stopped growing soon after the temperature was shifted to 44 degrees C but remained viable for several hours. Net RNA synthesis stopped within 20 min after the shift, while DNA and protein synthesis continued for over 60 min. At 44 degrees C, the half-life of total pulse-labeled RNA rose from 2.9 min in a wild-type strain to 5.9 min in the mrsC505 single mutant. In an rne-1 mrsC505 double mutant, the average half-life was 19.8 min. Inactivating mrsC significantly increased the half-lives of the trxA, cat, secG, and kan mRNAs, particularly in an mrsC505 pnp-7 rnb-500 rne-1 multiple mutant. In addition, Northern analysis showed dramatic stabilizations of full-length mRNAs in a variety of mrsC505 multiple mutants at 44 degrees C. These results suggest that MrsC, directly or indirectly, controls endonucleolytic processing of mRNAs that may be independent of the RNase E-PNPase-RhlB multiprotein complex.
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Affiliation(s)
- L L Granger
- Department of Genetics, University of Georgia, Athens 30602-7223, USA
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15
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Inada T, Nakamura Y. Lethal double-stranded RNA processing activity of ribonuclease III in the absence of suhB protein of Escherichia coli. Biochimie 1995; 77:294-302. [PMID: 8589060 DOI: 10.1016/0300-9084(96)88139-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The suhB gene of Escherichia coli has been defined by its mutant allele that suppresses other mutants in secY, rpoH, dnaB, and era. The suhB mutant by itself is cold sensitive, and is shown to have defects in protein synthesis. Starting with the suhB cold-sensitive mutant, cold-resistant suppressors were isolated. These suppressors mapped to the gene rnc encoding RNase III (a double-strand RNA-processing enzyme), and restored normal protein synthesis to the suhB mutants. Two known rnc mutations, rnc70 or rnc105, both defective in RNA cleavage activity, similarly restored growth of suhB. These rnc mutations did not alter the level of suhB expression. These results suggest that wild-type RNase III exerts a lethal effect on E coli upon depletion of SuhB at low temperatures. One explanation is to assume that the double-strand RNA-processing activity of RNase III itself is potentially lethal to E coli and the normal function of SuhB modulates the lethal action of RNase III.
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Affiliation(s)
- T Inada
- Department of Tumor Biology, University of Tokyo, Japan
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16
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Abstract
Post-transcriptional mechanisms operate in regulation of gene expression in bacteria, the amount of a given gene product being also dependent on the inactivation rate of its own message. Moreover, segmental differences in mRNA stability of polycistronic transcripts may be responsible for differential expression of genes clustered in operons. Given the absence of 5' to 3' exoribonucleolytic activities in prokaryotes, both endoribonucleases and 3' to 5' exoribonucleases are involved in chemical decay of mRNA. As the 3' to 5' exoribonucleolytic activities are readily blocked by stem-loop structures which are usual at the 3' ends of bacterial messages, the rate of decay is primarily determined by the rate of the first endonucleolytic cleavage within the transcripts, after which the resulting mRNA intermediates are degraded by the 3' to 5' exoribonucleases. Consequently, the stability of a given transcript is determined by the accessibility of suitable target sites to endonucleolytic activities. A considerable number of bacterial messages decay with a net 5' to 3' directionality. Two different alternative models have been proposed to explain such a finding, the first invoking the presence of functional coupling between degradation and the movement of the ribosomes along the transcripts, the second one implying the existence of a 5' to 3' processive '5' binding nuclease'. The different systems by which these two current models of mRNA decay have been tested will be presented with particular emphasis on polycistronic transcripts.
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Affiliation(s)
- P Alifano
- Dipartimento di Biologia e Patologia Cellulare e Molecolare L. Califano, Università di Napoli Federico II, Italy
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17
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Babitzke P, Granger L, Olszewski J, Kushner SR. Analysis of mRNA decay and rRNA processing in Escherichia coli multiple mutants carrying a deletion in RNase III. J Bacteriol 1993; 175:229-39. [PMID: 8416898 PMCID: PMC196118 DOI: 10.1128/jb.175.1.229-239.1993] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
RNase III is an endonuclease involved in processing both rRNA and certain mRNAs. To help determine whether RNase III (rnc) is required for general mRNA turnover in Escherichia coli, we have created a deletion-insertion mutation (delta rnc-38) in the structural gene. In addition, a series of multiple mutant strains containing deficiencies in RNase II (rnb-500), polynucleotide phosphorylase (pnp-7 or pnp-200), RNase E (rne-1 or rne-3071), and RNase III (delta rnc-38) were constructed. The delta rnc-38 single mutant was viable and led to the accumulation of 30S rRNA precursors, as has been previously observed with the rnc-105 allele (P. Gegenheimer, N. Watson, and D. Apirion, J. Biol. Chem. 252:3064-3073, 1977). In the multiple mutant strains, the presence of the delta rnc-38 allele resulted in the more rapid decay of pulse-labeled RNA but did not suppress conditional lethality, suggesting that the lethality associated with altered mRNA turnover may be due to the stabilization of specific mRNAs. In addition, these results indicate that RNase III is probably not required for general mRNA decay. Of particular interest was the observation that the delta rnc-38 rne-1 double mutant did not accumulate 30S rRNA precursors at 30 degrees C, while the delta rnc-38 rne-3071 double mutant did. Possible explanations of these results are discussed.
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Affiliation(s)
- P Babitzke
- Department of Genetics, University of Georgia, Athens 30602
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18
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Andersen JT, Poulsen P, Jensen KF. Attenuation in the rph-pyrE operon of Escherichia coli and processing of the dicistronic mRNA. EUROPEAN JOURNAL OF BIOCHEMISTRY 1992; 206:381-90. [PMID: 1375912 DOI: 10.1111/j.1432-1033.1992.tb16938.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
We have substituted on a plasmid the native promoter of the Escherichia coli rph-pyrE operon with an inducible transcription-initiation signal. The plasmid was used to study the mRNA chains derived from the operon at different intracellular concentrations of UTP and as a function of time following induction of transcription. The results showed that dicistronic rph-pyrE mRNA was formed when the UTP pool was low, and that a monocistronic rph mRNa was the major transcription product in high-UTP pools, thus supporting an UTP-controlled attenuation mechanism for regulation of pyrE gene expression. However, the dicistronic rph-pyrE transcript was rapidly processed into two monocistronic mRNA units, and a cleavage site was mapped near the attenuator in the intercistronic region, close to the site where transcription was terminated in high-UTP pools. Furthermore, the major 3' end of the pyrE mRNA was mapped near a palindromic structure of similarity to the family of repetitive extragenic palindromic sequences, 35 nucleotide residues after stop codon of the pryE gene.
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MESH Headings
- Base Sequence
- Blotting, Northern
- Escherichia coli/enzymology
- Escherichia coli/genetics
- Gene Expression Regulation, Bacterial
- Gene Expression Regulation, Enzymologic
- Genes, Bacterial
- Molecular Sequence Data
- Operon
- Orotate Phosphoribosyltransferase/biosynthesis
- Orotate Phosphoribosyltransferase/genetics
- Plasmids
- Promoter Regions, Genetic
- RNA Processing, Post-Transcriptional
- RNA, Bacterial/genetics
- RNA, Bacterial/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Terminator Regions, Genetic
- Transcription, Genetic
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Affiliation(s)
- J T Andersen
- Institute of Biological Chemistry B, University of Copenhagen, Denmark
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19
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Srivastava RA, Srivastava N, Apirion D. Characterization of the RNA processing enzyme RNase III from wild type and overexpressing Escherichia coli cells in processing natural RNA substrates. THE INTERNATIONAL JOURNAL OF BIOCHEMISTRY 1992; 24:737-49. [PMID: 1375563 DOI: 10.1016/0020-711x(92)90007-n] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
1. A precursor to small stable RNA, 10Sa RNA, accumulates in large amounts in a temperature sensitive RNase E mutant at non-permissive temperatures, and somewhat in an rnc (RNase III-) mutant, but not in an RNase P- mutant (rnp) or wild type E. coli cells. 2. Since p10Sa RNA was not processed by purified RNase E and III in customary assay conditions, we purified p10Sa RNA processing activity about 700-fold from wild type E. coli cells. 3. Processing of p10Sa RNA by this enzyme shows an absolute requirement for a divalent cation with a strong preference for Mn2+ over Mg2+. Other divalent cations could not replace Mn2+. 4. Monovalent cations (NH+4, Na+, K+) at a concentration of 20 mM stimulated the processing of p10Sa RNA and a temperature of 37 degrees C and pH range of 6.8-8.2 were found to be optimal. 5. The enzyme retained half of its p10Sa RNA processing activity after 30 min incubation at 50 degrees C. 6. Further characterization of this activity indicated that it is RNase III. 7. To further confirm that the p10Sa RNA processing activity is RNase III, we overexpressed the RNase III gene in an E. coli cells that lacks RNase III activity (rnc mutant) and RNase III was purified using one affinity column, agarose.poly(I).poly(C). 8. This RNase III preparation processed p10Sa RNA in a similar way as observed using the p10Sa RNA processing activity purified from wild type E. coli cells, confirming that the first step of p10Sa RNA processing is carried out by RNase III.
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Affiliation(s)
- R A Srivastava
- Department of Molecular Microbiology, Washington University School of Medicine, St Louis, MO 63110
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20
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Takata R, Izuhara M, Akiyama K. Processing in the 5' region of the pnp transcript facilitates the site-specific endonucleolytic cleavages of mRNA. Nucleic Acids Res 1992; 20:847-50. [PMID: 1371867 PMCID: PMC312027 DOI: 10.1093/nar/20.4.847] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The primary transcript of pnp, the gene encoding polynucleotide phosphorylase in Escherichia coli, is processed in the 5' end region by ribonuclease III (RNase III). The unprocessed transcript shows enhanced stability compared with the processed transcript. We report here that, unlike the processed transcript, the unprocessed pnp transcript did not accept endonucleolytic attack at, at least, five cleavage sites. Sequencing analysis of the four cleavage products shows no sequence specific to all these sites, but AU rich stretches were observed at three sites.
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Affiliation(s)
- R Takata
- Department of Biotechnology, College of Agriculture, Ehime University, Japan
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21
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Altuvia S, Kornitzer D, Kobi S, Oppenheim AB. Functional and structural elements of the mRNA of the cIII gene of bacteriophage lambda. J Mol Biol 1991; 218:723-33. [PMID: 1827163 DOI: 10.1016/0022-2836(91)90261-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The bacteriophage lambda cIII gene product is an early regulatory protein that participates in the lysis-lysogeny decision of the phage following infection. We have previously shown that the translation of the cIII gene is determined by two unique factors: (1) efficient expression is dependent upon the presence of RNaseIII in the cell; (2) alternative mRNA structures of the cIII coding region determine the rate of its translation initiation. In this study we demonstrate the presence of the alternative mRNA structures in vivo. The presence of minor RNaseIII cleavage sites within this region indicate that RNaseIII can differentiate between the two alternative structures. We localize by a deletion analysis the RNaseIII responsive element to the cIII coding region, and suggest that regulation of cIII translation by RNaseIII is achieved through binding to the alternative structures region of the mRNA.
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Affiliation(s)
- S Altuvia
- Department of Molecular Genetics, Hebrew University-Hadassah Medical School, Jerusalem, Israel
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22
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Lerner CG, Inouye M. Pleiotropic changes resulting from depletion of Era, an essential GTP-binding protein in Escherichia coli. Mol Microbiol 1991; 5:951-7. [PMID: 1906969 DOI: 10.1111/j.1365-2958.1991.tb00770.x] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Phenotypic analysis of a temperature-sensitive era mutant strain indicates that Escherichia coli cells depleted of Era undergo many physiological changes. At 43 degrees C, a completely non-permissive temperature, growth is arrested because of loss of the gene and depletion of the Era protein. Depletion of Era at 43 degrees C results in depressed synthesis of heat-shock proteins DnaK, GroEL/ES, D33.4 and C62.5, lack of thermal induction of ppGpp pool levels, and increased capacity for carbon source metabolism through the citric acid cycle. Thus, in addition to inhibition of cell growth and viability, loss of Era function results in pleiotropic changes including abnormal adaptation to thermal stress.
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Affiliation(s)
- C G Lerner
- Department of Biochemistry, Robert Wood Johnson Medical School, Rutgers University of Medicine and Dentistry of New Jersey, Piscataway 08854-5635
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23
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Izuhara M, Takamune K, Takata R. Cloning and sequencing of an Escherichia coli K12 gene which encodes a polypeptide having similarity to the human ferritin H subunit. MOLECULAR & GENERAL GENETICS : MGG 1991; 225:510-3. [PMID: 2017145 DOI: 10.1007/bf00261694] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Using lambda phage clones containing segments of the Escherichia coli K12 chromosome as hybridization probes, we found one gene at 42 min on the E. coli chromosome map, the expression of which was affected by RNase III. The sequence of the DNA fragment containing this gene (gen-165) revealed the presence of an open reading frame encoding a polypeptide of 165 amino acid residues. The amino acid sequence deduced from the nucleotide sequence exhibited a remarkable similarity to that of the human ferritin H chain.
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Affiliation(s)
- M Izuhara
- Department of Biology, Saga Medical School, Nabeshima, Japan
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24
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Régnier P, Grunberg-Manago M. RNase III cleavages in non-coding leaders of Escherichia coli transcripts control mRNA stability and genetic expression. Biochimie 1990; 72:825-34. [PMID: 2085545 DOI: 10.1016/0300-9084(90)90192-j] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The primary transcripts of the rpsO-pnp, rnc-era-recO and metY-nusA-infB operons of E coli are each processed by RNase III, upstream of the first translated gene, in hair-pin structures formed by the 5' non-coding leader. The mRNAs of the 3 operons, of which the 5' terminal motifs have been removed by RNase III, decay significantly more rapidly than the uncut transcripts which accumulate in the RNase III deficient strain. The rapid decay of a primary transcript of the metY-nusA-infB operon, initiated at a secondary promoter in the vicinity of the RNase III sites, suggests that the 5' features upstream of the RNase III cutting sites are responsible for the stability of the uncut RNAs. RNase III autocontrols its own expression by removing the 5' motif which stabilizes its mRNA. Similarly, the synthesis of polynucleotide phosphorylase and of protein Era are also controlled by RNase III cleavages which trigger the degradation of their messengers. The role of RNase III in the regulation of gene expression and the possible mechanisms of mRNA stabilization and of 5' to 3' decay initiated by RNase III processing are discussed.
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25
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Chen SM, Takiff HE, Barber AM, Dubois GC, Bardwell JC, Court DL. Expression and characterization of RNase III and Era proteins. Products of the rnc operon of Escherichia coli. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)39884-9] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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26
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Takata R, Izuhara M, Hori K. Differential degradation of the Escherichia coli polynucleotide phosphorylase mRNA. Nucleic Acids Res 1989; 17:7441-51. [PMID: 2477797 PMCID: PMC334822 DOI: 10.1093/nar/17.18.7441] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The transcript covering pnp, the gene encoding polynucleotide phosphorylase, is processed by RNaseIII at the 5'-upstream site of the pnp gene. In the RNaseIII-deficient strain, three species of the unprocessed transcript with different lengths could be detected. In this study, the stability of each transcript was analyzed by SI nuclease protection assay. The results show that the half-lives of the unprocessed transcripts are 8 min, whereas the half-life of the processed transcript is 1.5 min. It is also shown that the 5' segment of the unprocessed transcripts is more stable than the middle or the 3' segment.
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Affiliation(s)
- R Takata
- Department of Biology, Saga Medical School, Japan
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27
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Inada T, Kawakami K, Chen SM, Takiff HE, Court DL, Nakamura Y. Temperature-sensitive lethal mutant of era, a G protein in Escherichia coli. J Bacteriol 1989; 171:5017-24. [PMID: 2527846 PMCID: PMC210312 DOI: 10.1128/jb.171.9.5017-5024.1989] [Citation(s) in RCA: 60] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The era gene of Escherichia coli encodes a GTP-binding protein which has similarities to elongation factor Tu and the Saccharomyces cerevisiae RAS protein. To investigate its function, mutations affecting era were isolated. A mini-Tn10 insertion, which truncated 22 amino acids from the COOH end of Era, did not affect cell growth. By using this mini-Tn10 insert as a coselectable marker, a temperature-sensitive lethal era mutant was isolated by localized mutagenesis using P1 phage transduction. A single-base G to A change was found at position 23, causing a tyrosine residue to be substituted for the cysteine residue at position 8 (era-770), in addition to the COOH-terminal mini-Tn10 disruption. Both alterations were necessary for the temperature-sensitive phenotype. Purified Era-770 mutant protein exhibited reduced binding to GTP compared with that of the wild-type Era protein.
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Affiliation(s)
- T Inada
- Department of Tumor Biology, University of Tokyo, Japan
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28
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Hwang SPL, Eisenberg M, Binder R, Shelness GS, Williams DL. Predicted structures of apolipoprotein II mRNA constrained by nuclease and dimethyl sulfate reactivity: stable secondary structures occur predominantly in local domains via intraexonic base pairing. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)83197-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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29
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Abstract
RNase III, an Escherichia coli double-stranded endoribonuclease, is known to be involved in maturation of rRNA and regulation of several bacteriophage and Escherichia coli genes. Clones of the region of the E. coli chromosome containing the gene for RNase III (rnc) were obtained by screening genomic libraries in lambda with DNA known to map near rnc. A phage clone with the rnc region was randomly mutagenized with a delta Tn10 element, and the insertions were recombined onto the chromosome, generating a series of strains with delta Tn10 insertions in the rnc region. Two insertions that had Rnc- phenotypes were located. One of them lay in the rnc gene, and one was in the rnc leader sequence. Polarity studies showed that rnc is in an operon with two other genes, era and recO. The sequence of the recO gene beyond era indicated it could encode a protein of approximately 26 kilodaltons and, like rnc and era, had codon usage consistent with a low level of expression. Experiments using antibiotic cassettes to disrupt the genes rnc, era, and recO showed that era is essential for E. coli growth but that rnc and recO are dispensable.
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Affiliation(s)
- H E Takiff
- Laboratory of Molecular Oncology, National Cancer Institute-Frederick Cancer Research Facility, Maryland 21701
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