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Shore SFH, Leinberger FH, Fozo EM, Berghoff BA. Type I toxin-antitoxin systems in bacteria: from regulation to biological functions. EcoSal Plus 2024:eesp00252022. [PMID: 38767346 DOI: 10.1128/ecosalplus.esp-0025-2022] [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: 09/29/2023] [Accepted: 04/11/2024] [Indexed: 05/22/2024]
Abstract
Toxin-antitoxin systems are ubiquitous in the prokaryotic world and widely distributed among chromosomes and mobile genetic elements. Several different toxin-antitoxin system types exist, but what they all have in common is that toxin activity is prevented by the cognate antitoxin. In type I toxin-antitoxin systems, toxin production is controlled by an RNA antitoxin and by structural features inherent to the toxin messenger RNA. Most type I toxins are small membrane proteins that display a variety of cellular effects. While originally discovered as modules that stabilize plasmids, chromosomal type I toxin-antitoxin systems may also stabilize prophages, or serve important functions upon certain stress conditions and contribute to population-wide survival strategies. Here, we will describe the intricate RNA-based regulation of type I toxin-antitoxin systems and discuss their potential biological functions.
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Affiliation(s)
- Selene F H Shore
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee, USA
| | - Florian H Leinberger
- Institute for Microbiology and Molecular Biology, Justus-Liebig University, Giessen, Germany
| | - Elizabeth M Fozo
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee, USA
| | - Bork A Berghoff
- Institute for Microbiology and Molecular Biology, Justus-Liebig University, Giessen, Germany
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2
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Bonabal S, Darfeuille F. Preventing toxicity in toxin-antitoxin systems: An overview of regulatory mechanisms. Biochimie 2024; 217:95-105. [PMID: 37473832 DOI: 10.1016/j.biochi.2023.07.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Revised: 07/13/2023] [Accepted: 07/17/2023] [Indexed: 07/22/2023]
Abstract
Toxin-antitoxin systems (TAs) are generally two-component genetic modules present in almost every prokaryotic genome. The production of the free and active toxin is able to disrupt key cellular processes leading to the growth inhibition or death of its host organism in absence of its cognate antitoxin. The functions attributed to TAs rely on this lethal phenotype ranging from mobile genetic elements stabilization to phage defense. Their abundance in prokaryotic genomes as well as their lethal potential make them attractive targets for new antibacterial strategies. The hijacking of TAs requires a deep understanding of their regulation to be able to design such approach. In this review, we summarize the accumulated knowledge on how bacteria cope with these toxic genes in their genome. The characterized TAs can be grouped based on the way they prevent toxicity. Some systems rely on a tight control of the expression to prevent the production of the toxin while others control the activity of the toxin at the post-translational level.
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Affiliation(s)
- Simon Bonabal
- University of Bordeaux, INSERM U1212, CNRS UMR 5320, ARNA Laboratory, F-33000, Bordeaux, France
| | - Fabien Darfeuille
- University of Bordeaux, INSERM U1212, CNRS UMR 5320, ARNA Laboratory, F-33000, Bordeaux, France.
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Regulation of Mannitol Metabolism in Enterococcus faecalis and Association with parEF0409 Toxin-Antitoxin Locus Function. J Bacteriol 2022; 204:e0004722. [PMID: 35404112 DOI: 10.1128/jb.00047-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The parEF0409 type I toxin-antitoxin locus is situated between genes for two paralogous mannitol family phosphoenolpyruvate phosphotransferase systems (PTSs). In order to address the possibility that parEF0409 function was associated with sugar metabolism, genetic and phenotypic analyses were performed on the flanking genes. It was found that the genes were transcribed as two operons: the downstream operon essential for mannitol transport and metabolism and the upstream operon performing a regulatory function. In addition to genes for the PTS components, the upstream operon harbors a gene similar to mtlR, the key regulator of mannitol metabolism in other Gram-positive bacteria. We confirmed that this gene is essential for the regulation of the downstream operon and identified putative phosphorylation sites required for carbon catabolite repression and mannitol-specific regulation. Genomic comparisons revealed that this dual-operon organization of mannitol utilization genes is uncommon in enterococci and that the association with a toxin-antitoxin system is unique to Enterococcus faecalis. Finally, we consider possible links between parEF0409 function and mannitol utilization. IMPORTANCE Enterococcus faecalis is both a common member of the human gut microbiota and an opportunistic pathogen. Its evolutionary success is partially due to its metabolic flexibility, in particular its ability to import and metabolize a wide variety of sugars. While a large number of phosphoenolpyruvate phosphotransferase sugar transport systems have been identified in the E. faecalis genome bioinformatically, the specificity and regulation of most of these systems remain undetermined. Here, we characterize a complex system of two operons flanking a type I toxin-antitoxin system required for the transport and metabolism of the common dietary sugar mannitol. We also determine the phylogenetic distribution of mannitol utilization genes in the enterococcal genus and discuss the significance of the association with toxin-antitoxin systems.
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Sarpong DD, Murphy ER. RNA Regulated Toxin-Antitoxin Systems in Pathogenic Bacteria. Front Cell Infect Microbiol 2021; 11:661026. [PMID: 34084755 PMCID: PMC8167048 DOI: 10.3389/fcimb.2021.661026] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2021] [Accepted: 04/29/2021] [Indexed: 01/05/2023] Open
Abstract
The dynamic host environment presents a significant hurdle that pathogenic bacteria must overcome to survive and cause diseases. Consequently, these organisms have evolved molecular mechanisms to facilitate adaptation to environmental changes within the infected host. Small RNAs (sRNAs) have been implicated as critical regulators of numerous pathways and systems in pathogenic bacteria, including that of bacterial Toxin-Antitoxin (TA) systems. TA systems are typically composed of two factors, a stable toxin, and a labile antitoxin which functions to protect against the potentially deleterious activity of the associated toxin. Of the six classes of bacterial TA systems characterized to date, the toxin component is always a protein. Type I and Type III TA systems are unique in that the antitoxin in these systems is an RNA molecule, whereas the antitoxin in all other TA systems is a protein. Though hotly debated, the involvement of TA systems in bacterial physiology is recognized by several studies, with the Type II TA system being the most extensively studied to date. This review focuses on RNA-regulated TA systems, highlighting the role of Type I and Type III TA systems in several pathogenic bacteria.
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Affiliation(s)
- David D. Sarpong
- Department of Biological Sciences, Ohio University, Athens, OH, United States
- Infectious and Tropical Diseases Institute, Ohio University, Athens, OH, United States
- Molecular and Cellular Biology Program, Ohio University, Athens, OH, United States
| | - Erin R. Murphy
- Infectious and Tropical Diseases Institute, Ohio University, Athens, OH, United States
- Molecular and Cellular Biology Program, Ohio University, Athens, OH, United States
- Department of Biomedical Sciences, Ohio University, Heritage College of Osteopathic Medicine, Athens, OH, United States
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5
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Weaver K. The Fst/Ldr Family of Type I TA System Toxins: Potential Roles in Stress Response, Metabolism and Pathogenesis. Toxins (Basel) 2020; 12:toxins12080474. [PMID: 32722354 PMCID: PMC7472228 DOI: 10.3390/toxins12080474] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 07/20/2020] [Accepted: 07/23/2020] [Indexed: 12/27/2022] Open
Abstract
The parpAD1 locus was the first type I toxin-antitoxin (TA) system described in Gram-positive bacteria and was later determined to be the founding member of a widely distributed family of plasmid- and chromosomally encoded TA systems. Indeed, homology searches revealed that the toxin component, FstpAD1, is a member of the Fst/Ldr superfamily of peptide toxins found in both Gram-positive and Gram-negative bacteria. Regulation of the Fst and Ldr toxins is distinct in their respective Gram-positive and Gram-negative hosts, but the effects of ectopic over-expression are similar. While, the plasmid versions of these systems appear to play the canonical role of post-segregational killing stability mechanisms, the function of the chromosomal systems remains largely obscure. At least one member of the family has been suggested to play a role in pathogenesis in Staphylococcus aureus, while the regulation of several others appear to be tightly integrated with genes involved in sugar metabolism. After a brief discussion of the regulation and function of the foundational parpAD1 locus, this review will focus on the current information available on potential roles of the chromosomal homologs.
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Affiliation(s)
- Keith Weaver
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069, USA
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6
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Abstract
The study of the genetics of enterococci has focused heavily on mobile genetic elements present in these organisms, the complex regulatory circuits used to control their mobility, and the antibiotic resistance genes they frequently carry. Recently, more focus has been placed on the regulation of genes involved in the virulence of the opportunistic pathogenic species Enterococcus faecalis and Enterococcus faecium. Little information is available concerning fundamental aspects of DNA replication, partition, and division; this article begins with a brief overview of what little is known about these issues, primarily by comparison with better-studied model organisms. A variety of transcriptional and posttranscriptional mechanisms of regulation of gene expression are then discussed, including a section on the genetics and regulation of vancomycin resistance in enterococci. The article then provides extensive coverage of the pheromone-responsive conjugation plasmids, including sections on regulation of the pheromone response, the conjugative apparatus, and replication and stable inheritance. The article then focuses on conjugative transposons, now referred to as integrated, conjugative elements, or ICEs, and concludes with several smaller sections covering emerging areas of interest concerning the enterococcal mobilome, including nonpheromone plasmids of particular interest, toxin-antitoxin systems, pathogenicity islands, bacteriophages, and genome defense.
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Type I Toxin-Antitoxin Systems: Regulating Toxin Expression via Shine-Dalgarno Sequence Sequestration and Small RNA Binding. Microbiol Spectr 2019; 6. [PMID: 30051800 DOI: 10.1128/microbiolspec.rwr-0030-2018] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Toxin-antitoxin (TA) systems are small genetic loci composed of two adjacent genes: a toxin and an antitoxin that prevents toxin action. Despite their wide distribution in bacterial genomes, the reasons for TA systems being on chromosomes remain enigmatic. In this review, we focus on type I TA systems, composed of a small antisense RNA that plays the role of an antitoxin to control the expression of its toxin counterpart. It does so by direct base-pairing to the toxin-encoding mRNA, thereby inhibiting its translation and/or promoting its degradation. However, in many cases, antitoxin binding is not sufficient to avoid toxicity. Several cis-encoded mRNA elements are also required for repression, acting to uncouple transcription and translation via the sequestration of the ribosome binding site. Therefore, both antisense RNA binding and compact mRNA folding are necessary to tightly control toxin synthesis and allow the presence of these toxin-encoding systems on bacterial chromosomes.
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Examination of Enterococcus faecalis Toxin-Antitoxin System Toxin Fst Function Utilizing a Pheromone-Inducible Expression Vector with Tight Repression and Broad Dynamic Range. J Bacteriol 2017; 199:JB.00065-17. [PMID: 28348028 DOI: 10.1128/jb.00065-17] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2017] [Accepted: 03/21/2017] [Indexed: 01/02/2023] Open
Abstract
Tools for regulated gene expression in Enterococcus faecalis are extremely limited. In this report, we describe the construction of an expression vector for E. faecalis, designated pCIE, utilizing the PQ pheromone-responsive promoter of plasmid pCF10. We demonstrate that this promoter is tightly repressed, responds to nanogram quantities of the peptide pheromone, and has a large dynamic range. To demonstrate its utility, the promoter was used to control expression of the toxic peptides of two par family toxin-antitoxin (TA) loci present in E. faecalis, parpAD1 of the pAD1 plasmid and parEF0409 located on the E. faecalis chromosome. The results demonstrated differences in the modes of regulation of toxin expression and in the effects of toxins of these two related systems. We anticipate that this vector will be useful for further investigation of par TA system function as well as the regulated expression of other genes in E. faecalisIMPORTANCEE. faecalis is an important nosocomial pathogen and a model organism for examination of the genetics and physiology of Gram-positive cocci. While numerous genetic tools have been generated for the manipulation of this organism, vectors for the regulated expression of cloned genes remain limited by high background expression and the use of inducers with undesirable effects on the cell. Here we demonstrate that the PQ pheromone-responsive promoter is repressed tightly enough to allow cloning of TA system toxins and evaluate their effects at very low induction levels. This tool will allow us to more fully examine TA system function in E. faecalis and to further elucidate its potential roles in cell physiology.
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Structure, Biology, and Therapeutic Application of Toxin-Antitoxin Systems in Pathogenic Bacteria. Toxins (Basel) 2016; 8:toxins8100305. [PMID: 27782085 PMCID: PMC5086665 DOI: 10.3390/toxins8100305] [Citation(s) in RCA: 75] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 10/17/2016] [Accepted: 10/18/2016] [Indexed: 01/09/2023] Open
Abstract
Bacterial toxin–antitoxin (TA) systems have received increasing attention for their diverse identities, structures, and functional implications in cell cycle arrest and survival against environmental stresses such as nutrient deficiency, antibiotic treatments, and immune system attacks. In this review, we describe the biological functions and the auto-regulatory mechanisms of six different types of TA systems, among which the type II TA system has been most extensively studied. The functions of type II toxins include mRNA/tRNA cleavage, gyrase/ribosome poison, and protein phosphorylation, which can be neutralized by their cognate antitoxins. We mainly explore the similar but divergent structures of type II TA proteins from 12 important pathogenic bacteria, including various aspects of protein–protein interactions. Accumulating knowledge about the structure–function correlation of TA systems from pathogenic bacteria has facilitated a novel strategy to develop antibiotic drugs that target specific pathogens. These molecules could increase the intrinsic activity of the toxin by artificially interfering with the intermolecular network of the TA systems.
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10
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Ribonucleases, antisense RNAs and the control of bacterial plasmids. Plasmid 2015; 78:26-36. [DOI: 10.1016/j.plasmid.2014.09.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Revised: 09/16/2014] [Accepted: 09/18/2014] [Indexed: 12/23/2022]
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11
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Durand S, Jahn N, Condon C, Brantl S. Type I toxin-antitoxin systems inBacillus subtilis. RNA Biol 2014; 9:1491-7. [DOI: 10.4161/rna.22358] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
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12
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Weaver KE. The Type I toxin-antitoxin par locus from Enterococcus faecalis plasmid pAD1: RNA regulation by both cis- and trans-acting elements. Plasmid 2014; 78:65-70. [PMID: 25312777 DOI: 10.1016/j.plasmid.2014.10.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2014] [Revised: 09/30/2014] [Accepted: 10/04/2014] [Indexed: 01/13/2023]
Abstract
The pAD1 par determinant was the first Type I toxin-antitoxin system identified in Gram-positive bacteria and has recently been shown to be the prototype of a family of loci that is widespread in these organisms. All family members have (i) convergently transcribed toxin message and regulatory RNAs, (ii) three non-contiguous complementary regions for potential interaction, and (iii) intramolecular structures within the toxin message that modulate translation and transcript stability. Therefore, the detailed information available on the par locus provides a paradigm for studying the function and mechanism of regulation of the related loci.
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Affiliation(s)
- Keith E Weaver
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069, USA.
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13
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Wen J, Fozo EM. sRNA antitoxins: more than one way to repress a toxin. Toxins (Basel) 2014; 6:2310-35. [PMID: 25093388 PMCID: PMC4147584 DOI: 10.3390/toxins6082310] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Revised: 07/15/2014] [Accepted: 07/17/2014] [Indexed: 11/16/2022] Open
Abstract
Bacterial toxin-antitoxin loci consist of two genes: one encodes a potentially toxic protein, and the second, an antitoxin to repress its function or expression. The antitoxin can either be an RNA or a protein. For type I and type III loci, the antitoxins are RNAs; however, they have very different modes of action. Type I antitoxins repress toxin protein expression through interacting with the toxin mRNA, thereby targeting the mRNA for degradation or preventing its translation or both; type III antitoxins directly bind to the toxin protein, sequestering it. Along with these two very different modes of action for the antitoxin, there are differences in the functions of the toxin proteins and the mobility of these loci between species. Within this review, we discuss the major differences as to how the RNAs repress toxin activity, the potential consequences for utilizing different regulatory strategies, as well as the confirmed and potential biological roles for these loci across bacterial species.
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Affiliation(s)
- Jia Wen
- Department of Microbiology, University of Tennessee, M409 Walters Life Sciences, Knoxville, TN 37996, USA.
| | - Elizabeth M Fozo
- Department of Microbiology, University of Tennessee, M409 Walters Life Sciences, Knoxville, TN 37996, USA.
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14
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Abstract
Type I toxin–antitoxin systems encoded on bacterial chromosomes became the focus of research during the past years. However, little is known in terms of structural requirements, kinetics of interaction with their targets and regulatory mechanisms of the antitoxin RNAs. Here, we present a combined in vitro and in vivo analysis of the bsrG/SR4 type I toxin–antitoxin system from Bacillus subtilis. The secondary structures of SR4 and bsrG mRNA and of the SR4/bsrG RNA complex were determined, apparent binding rate constants calculated and functional segments required for complex formation narrowed down. The initial contact between SR4 and its target was shown to involve the SR4 terminator loop and loop 3 of bsrG mRNA. Additionally, a contribution of the stem of SR4 stem-loop 3 to target binding was found. On SR4/bsrG complex formation, a 4 bp double-stranded region sequestering the bsrG Shine Dalgarno (SD) sequence was extended to 8 bp. Experimental evidence was obtained that this extended region caused translation inhibition of bsrG mRNA. Therefore, we conclude that SR4 does not only promote degradation of the toxin mRNA but also additionally inhibit its translation. This is the first case of a dual-acting antitoxin RNA.
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Affiliation(s)
| | - Sabine Brantl
- *To whom correspondence should be addressed. Tel: +49 3641 949570; Fax: +49 3641 949302;
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15
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Mruk I, Kobayashi I. To be or not to be: regulation of restriction-modification systems and other toxin-antitoxin systems. Nucleic Acids Res 2013; 42:70-86. [PMID: 23945938 PMCID: PMC3874152 DOI: 10.1093/nar/gkt711] [Citation(s) in RCA: 164] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
One of the simplest classes of genes involved in programmed death is that containing the toxin–antitoxin (TA) systems of prokaryotes. These systems are composed of an intracellular toxin and an antitoxin that neutralizes its effect. These systems, now classified into five types, were initially discovered because some of them allow the stable maintenance of mobile genetic elements in a microbial population through postsegregational killing or the death of cells that have lost these systems. Here, we demonstrate parallels between some TA systems and restriction–modification systems (RM systems). RM systems are composed of a restriction enzyme (toxin) and a modification enzyme (antitoxin) and limit the genetic flux between lineages with different epigenetic identities, as defined by sequence-specific DNA methylation. The similarities between these systems include their postsegregational killing and their effects on global gene expression. Both require the finely regulated expression of a toxin and antitoxin. The antitoxin (modification enzyme) or linked protein may act as a transcriptional regulator. A regulatory antisense RNA recently identified in an RM system can be compared with those RNAs in TA systems. This review is intended to generalize the concept of TA systems in studies of stress responses, programmed death, genetic conflict and epigenetics.
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Affiliation(s)
- Iwona Mruk
- Department of Microbiology, University of Gdansk, Wita Stwosza 59, Gdansk, 80-308, Poland, Department of Medical Genome Sciences, Graduate School of Frontier Sciences, University of Tokyo, Tokyo 108-8639, Japan and Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan
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16
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Werner G, Coque TM, Franz CMAP, Grohmann E, Hegstad K, Jensen L, van Schaik W, Weaver K. Antibiotic resistant enterococci-tales of a drug resistance gene trafficker. Int J Med Microbiol 2013; 303:360-79. [PMID: 23602510 DOI: 10.1016/j.ijmm.2013.03.001] [Citation(s) in RCA: 116] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Enterococci have been recognized as important hospital-acquired pathogens in recent years, and isolates of E. faecalis and E. faecium are the third- to fourth-most prevalent nosocomial pathogen worldwide. Acquired resistances, especially against penicilin/ampicillin, aminoglycosides (high-level) and glycopeptides are therapeutically important and reported in increasing numbers. On the other hand, isolates of E. faecalis and E. faecium are commensals of the intestines of humans, many vertebrate and invertebrate animals and may also constitute an active part of the plant flora. Certain enterococcal isolates are used as starter cultures or supplements in food fermentation and food preservation. Due to their preferred intestinal habitat, their wide occurrence, robustness and ease of cultivation, enterococci are used as indicators for fecal pollution assessing hygiene standards for fresh- and bathing water and they serve as important key indicator bacteria for various veterinary and human resistance surveillance systems. Enterococci are widely prevalent and genetically capable of acquiring, conserving and disseminating genetic traits including resistance determinants among enterococci and related Gram-positive bacteria. In the present review we aimed at summarizing recent advances in the current understanding of the population biology of enterococci, the role mobile genetic elements including plasmids play in shaping the population structure and spreading resistance. We explain how these elements could be classified and discuss mechanisms of plasmid transfer and regulation and the role and cross-talk of enterococcal isolates from food and food animals to humans.
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Affiliation(s)
- Guido Werner
- National Reference Centre for Stapyhlococci and Enterococci, Division of Nosocomial Pathogens and Antibiotic Resistances, Robert Koch Institute, Wernigerode Branch, Burgstr. 37, 38855 Wernigerode, Germany.
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17
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Liu MA, Kwong SM, Jensen SO, Brzoska AJ, Firth N. Biology of the staphylococcal conjugative multiresistance plasmid pSK41. Plasmid 2013; 70:42-51. [PMID: 23415796 DOI: 10.1016/j.plasmid.2013.02.001] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2012] [Revised: 02/01/2013] [Accepted: 02/03/2013] [Indexed: 11/27/2022]
Abstract
Plasmid pSK41 is a large, low-copy-number, conjugative plasmid from Staphylococcus aureus that is representative of a family of staphylococcal plasmids that confer multiple resistances to a wide range of antimicrobial agents. The plasmid consists of a conserved plasmid backbone containing the genes for plasmid housekeeping functions, which is punctuated by copies of IS257 that flank a Tn4001-hybrid structure and cointegrated plasmids that harbour resistance genes. This review summarises the current understanding of the biology of pSK41, focussing on the systems responsible for its replication, maintenance and transmission, and their regulation.
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Affiliation(s)
- Michael A Liu
- School of Biological Sciences, University of Sydney, NSW 2006, Australia
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18
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Weaver KE. The par toxin-antitoxin system from Enterococcus faecalis plasmid pAD1 and its chromosomal homologs. RNA Biol 2012; 9:1498-503. [PMID: 23059908 DOI: 10.4161/rna.22311] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The par post-segregational killing locus present on Enterococcus faecalis plasmid pAD1 was the first Type I toxin-antitoxin system described in Gram-positive bacteria. Translation of the 33 amino acid Fst toxin, encoded on RNA I, is suppressed by a 66 nucleotide regulatory RNA, RNA II. RNA I and RNA II are transcribed convergently and interact at dispersed regions of complementarity, establishing a stable complex that accumulates in plasmid-containing cells. RNA II is slowly removed from the complex, allowing translation of RNA I in plasmid-free segregants. Intramolecular structures are also important for regulating translation of RNA I. The Fst toxin contains a putative transmembrane domain and is believed to exert its function at the bacterial cytoplasmic membrane, although its precise target and mode of action have yet to be determined. Numerous chromosomal homologs of pAD1 par have been identified in Gram-positive bacteria suggesting that this locus may play important roles in cellular function.
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Affiliation(s)
- Keith E Weaver
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD USA.
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19
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Brantl S. Acting antisense: plasmid- and chromosome-encoded sRNAs from Gram-positive bacteria. Future Microbiol 2012; 7:853-71. [DOI: 10.2217/fmb.12.59] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
sRNAs that act by base pairing were first discovered in plasmids, phages and transposons, where they control replication, maintenance and transposition. Since 2001, however, computational searches were applied that led to the discovery of a plethora of sRNAs in bacterial chromosomes. Whereas the majority of these chromsome-encoded sRNAs have been investigated in Escherichia coli, Salmonella and other Gram-negative bacteria, only a few well-studied examples are known from Gram-positive bacteria. Here, the author summarizes our current knowledge on plasmid- and chromosome-encoded sRNAs from Gram-positive species, thereby focusing on regulatory mechanisms used by these RNAs and their biological role in complex networks. Furthermore, regulatory factors that control the expression of these RNAs will be discussed and differences between sRNAs from Gram-positive and Gram-negative bacteria highlighted. The main emphasis of this review is on sRNAs that act by base pairing (i.e., by an antisense mechanism). Thereby, both plasmid-encoded and chromosome-encoded sRNAs will be considered.
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Affiliation(s)
- Sabine Brantl
- AG Bakteriengenetik, Friedrich-Schiller-Universität Jena, Philosophenweg 12, D-07743 Jena, Germany
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Göbl C, Kosol S, Stockner T, Rückert HM, Zangger K. Solution structure and membrane binding of the toxin fst of the par addiction module. Biochemistry 2010; 49:6567-75. [PMID: 20677831 PMCID: PMC2914490 DOI: 10.1021/bi1005128] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
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The par toxin−antitoxin system is required for the stable inheritance of the plasmid pAD1 in its native host Enterococcus faecalis. It codes for the toxin Fst and a small antisense RNA which inhibits translation of toxin mRNA, and it is the only known antisense regulated toxin−antitoxin system in Gram-positive bacteria. This study presents the structure of the par toxin Fst, the first atomic resolution structure of a component of an antisense regulated toxin−antitoxin system. The mode of membrane binding was determined by relaxation enhancements in a paramagnetic environment and molecular dynamics simulation. Fst forms a membrane-binding α-helix in the N-terminal part and contains an intrinsically disordered region near the C-terminus. It binds in a transmembrane orientation with the C-terminus likely pointing toward the cytosol. Membrane-bound, α-helical peptides are frequently found in higher organisms as components of the innate immune system. Despite similarities to these antimicrobial peptides, Fst shows neither hemolytic nor antimicrobial activity when applied externally to a series of bacteria, fungal cells, and erythrocytes. Moreover, its charge distribution, orientation in the membrane, and structure distinguish it from antimicrobial peptides.
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Affiliation(s)
- Christoph Göbl
- Institute of Chemistry/Organic and Bioorganic Chemistry, University of Graz, Heinrichstrasse 28, A-8010 Graz, Austria
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21
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Jensen SO, Apisiridej S, Kwong SM, Yang YH, Skurray RA, Firth N. Analysis of the prototypical Staphylococcus aureus multiresistance plasmid pSK1. Plasmid 2010; 64:135-42. [PMID: 20547176 DOI: 10.1016/j.plasmid.2010.06.001] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Revised: 05/26/2010] [Accepted: 06/06/2010] [Indexed: 11/16/2022]
Abstract
The Staphylococcus aureus multiresistance plasmid pSK1 is the prototype of a family of structurally related plasmids that were first identified in epidemic S. aureus strains isolated in Australia during the 1980s and subsequently in Europe. Here we present the complete 28.15kb nucleotide sequence of pSK1 and discuss the genetic content and evolution of the 14kb region that is conserved throughout the pSK1 plasmid family. In addition to the previously characterized plasmid maintenance functions, this backbone region encodes 12 putative gene products, including a lipoprotein, teichoic acid translocation permease, cell wall anchored surface protein and an Fst-like toxin as part of a Type I toxin-antitoxin system. Furthermore, transcriptional profiling has revealed that plasmid carriage most likely has a minimal impact on the host, a factor that may contribute to the ability of pSK1 family plasmids to carry multiple resistance determinants.
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Affiliation(s)
- Slade O Jensen
- School of Biological Sciences, University of Sydney, New South Wales, Australia
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22
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Kwong SM, Jensen SO, Firth N. Prevalence of Fst-like toxin-antitoxin systems. MICROBIOLOGY-SGM 2010; 156:975-977. [PMID: 20150240 DOI: 10.1099/mic.0.038323-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Affiliation(s)
- Stephen M Kwong
- School of Biological Sciences, The University of Sydney, NSW 2006, Australia
| | - Slade O Jensen
- School of Biological Sciences, The University of Sydney, NSW 2006, Australia
| | - Neville Firth
- School of Biological Sciences, The University of Sydney, NSW 2006, Australia
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23
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Romby P, Charpentier E. An overview of RNAs with regulatory functions in gram-positive bacteria. Cell Mol Life Sci 2010; 67:217-37. [PMID: 19859665 PMCID: PMC11115938 DOI: 10.1007/s00018-009-0162-8] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2009] [Revised: 09/07/2009] [Accepted: 09/23/2009] [Indexed: 11/26/2022]
Abstract
During the last decade, RNA molecules with regulatory functions on gene expression have benefited from a renewed interest. In bacteria, recent high throughput computational and experimental approaches have led to the discovery that 10-20% of all genes code for RNAs with critical regulatory roles in metabolic, physiological and pathogenic processes. The trans-acting RNAs comprise the noncoding RNAs, RNAs with a short open reading frame and antisense RNAs. Many of these RNAs act through binding to their target mRNAs while others modulate protein activity or target DNA. The cis-acting RNAs include regulatory regions of mRNAs that can respond to various signals. These RNAs often provide the missing link between sensing changing conditions in the environment and fine-tuning the subsequent biological responses. Information on their various functions and modes of action has been well documented for gram-negative bacteria. Here, we summarize the current knowledge of regulatory RNAs in gram-positive bacteria.
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Affiliation(s)
- Pascale Romby
- Architecture et Réactivité de l’ARN, Université de Strasbourg, CNRS, IBMC, 15 rue René Descartes, 67084 Strasbourg, France
| | - Emmanuelle Charpentier
- Max F. Perutz Laboratories, University of Vienna, Dr. Bohrgasse 9, 1030 Vienna, Austria
- The Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University, 90187 Umeå, Sweden
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24
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Weaver KE, Reddy SG, Brinkman CL, Patel S, Bayles KW, Endres JL. Identification and characterization of a family of toxin-antitoxin systems related to the Enterococcus faecalis plasmid pAD1 par addiction module. MICROBIOLOGY-SGM 2009; 155:2930-2940. [PMID: 19542006 DOI: 10.1099/mic.0.030932-0] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The par locus of the Enterococcus faecalis plasmid pAD1 is an RNA-regulated addiction module encoding the peptide toxin Fst. Homology searches revealed that Fst belongs to a family of at least nine related peptides encoded on the chromosomes and plasmids of six different Gram-positive bacterial species. Comparison of an alignment of these peptides with the results of a saturation mutagenesis analysis indicated regions of the peptides important for biological function. Examination of the genetic context of the fst genes revealed that all of these peptides are encoded within par-like loci with conserved features similar to pAD1 par. All four Ent. faecalis family members were demonstrated to produce the expected toxin-encoding and regulatory RNA products. The locus from the Ent. faecalis plasmid pAMS1 was demonstrated to function as an addiction module and Fst was shown to be toxic to Staphylococcus aureus, suggesting that a plasmid-encoded module in that species is performing the same function. Thus, the pAD1-encoded par locus appears to be the prototype of a family of related loci found in several Gram-positive species.
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Affiliation(s)
- Keith E Weaver
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069, USA
| | - Shirisha G Reddy
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069, USA
| | - Cassandra L Brinkman
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069, USA
| | - Smita Patel
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069, USA
| | - Kenneth W Bayles
- Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE 68198, USA
| | - Jennifer L Endres
- Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE 68198, USA
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25
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Small toxic proteins and the antisense RNAs that repress them. Microbiol Mol Biol Rev 2009; 72:579-89, Table of Contents. [PMID: 19052321 DOI: 10.1128/mmbr.00025-08] [Citation(s) in RCA: 207] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
There has been a great expansion in the number of small regulatory RNAs identified in bacteria. Some of these small RNAs repress the synthesis of potentially toxic proteins. Generally the toxin proteins are hydrophobic and less than 60 amino acids in length, and the corresponding antitoxin small RNA genes are antisense to the toxin genes or share long stretches of complementarity with the target mRNAs. Given their short length, only a limited number of these type I toxin-antitoxin loci have been identified, but it is predicted that many remain to be found. Already their characterization has given insights into regulation by small RNAs, has suggested functions for the small toxic proteins at the cell membrane, and has led to practical applications for some of the type I toxin-antitoxin loci.
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26
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An intramolecular upstream helix ensures the stability of a toxin-encoding RNA in Enterococcus faecalis. J Bacteriol 2008; 191:1528-36. [PMID: 19103923 DOI: 10.1128/jb.01316-08] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The par stability determinant is required for the stable inheritance of the plasmid pAD1 in its native host, Enterococcus faecalis. It is the only antisense RNA-regulated addiction module identified to date in gram-positive bacteria. It encodes two small, convergently transcribed RNAs, RNA I and RNA II. RNA I encodes the Fst toxin and RNA II acts as the antitoxin by interacting with RNA I posttranscriptionally. As the toxin-encoding component of the system, it is important that RNA I is more stable than RNA II. This study reveals that a helix sequestering the 5' end of RNA I plays a crucial role in maintaining the stability of the RNA I. An adjacent structure previously determined to regulate Fst translation was not required to enhance stability. Results indicated that endoribonuclease J2 contributes significantly to the degradation of a mutant disrupting the upstream helix (UH) of RNA I in Bacillus subtilis. Finally, it was shown that interaction with RNA II stabilized the UH mutant of RNA I.
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27
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Translational regulation by an intramolecular stem-loop is required for intermolecular RNA regulation of the par addiction module. J Bacteriol 2008; 190:6076-83. [PMID: 18641135 DOI: 10.1128/jb.00660-08] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The par stability determinant of Enterococcus faecalis plasmid pAD1 is the only antisense RNA-regulated addiction module identified to date in gram-positive bacteria. par encodes two small, convergently transcribed RNAs, designated RNA I and RNA II, that function as the toxin (Fst)-encoding and antitoxin components, respectively. Previous work showed that structures at the 5' end of RNA I are important in regulating its translation. The work presented here reveals that a stem-loop sequestering the Fst ribosome binding site is required for translational repression but a helix sequestering the 5' end of RNA I is not. Furthermore, disruption of the stem-loop prevented RNA II-mediated repression of Fst translation in vivo. Finally, although Fst-encoding wild-type RNA I is not toxic in Escherichia coli, mutations affecting stem-loop stability resulted in toxicity in this host, presumably due to increased translation.
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28
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Clewell DB. Properties of Enterococcus faecalis plasmid pAD1, a member of a widely disseminated family of pheromone-responding, conjugative, virulence elements encoding cytolysin. Plasmid 2007; 58:205-27. [PMID: 17590438 DOI: 10.1016/j.plasmid.2007.05.001] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2007] [Revised: 05/02/2007] [Accepted: 05/12/2007] [Indexed: 11/23/2022]
Abstract
The 60-kb pAD1 represents a large and widely disseminated family of conjugative, pheromone-responding, virulence plasmids commonly found in clinical isolates of Enterococcus faecalis. It encodes a hemolysin/bacteriocin (cytolysin) shown to contribute to virulence in animal models, and the related bacteriocin is active against a wide variety of Gram-positive bacteria. This review summarizes what is currently known about the molecular biology of pAD1, including aspects of its cytolytic, UV-resistance, replication, maintenance, and conjugative properties.
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Affiliation(s)
- Don B Clewell
- Department of Biologic and Materials Sciences, School of Dentistry, The University of Michigan, Ann Arbor, MI 48109-1078, USA.
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29
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Weaver KE. Emerging plasmid-encoded antisense RNA regulated systems. Curr Opin Microbiol 2007; 10:110-6. [PMID: 17376732 DOI: 10.1016/j.mib.2007.03.002] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2006] [Accepted: 03/08/2007] [Indexed: 11/23/2022]
Abstract
Classic antisense RNA research has focused on detailed examination of a few plasmid-encoded systems whilst more recent efforts have focused on chromosomally encoded small RNAs. Recent work on newly identified plasmid-encoded antisense RNAs suggest that there is still much to learn from them about the versatility of regulatory RNAs. The alpha-proteobacterial repABC plasmids produce an antisense RNA that regulates the replication initiator independently of the partition proteins encoded in the same operon. The Staphylococcus aureus plasmid pSK41 produces an antisense RNA that regulates the replication initiator protein by a translational attenuation mechanism. Enterococcus faecalis pheromone-responsive plasmids produce plasmid-specific variants of an antisense RNA that regulates conjugation structural genes by a transcriptional attenuation mechanism. E. faecalis plasmid pAD1 encodes an antisense RNA-regulated addiction module that combines features of classic plasmid-encoded and trans-regulated chromosomally encoded antisense systems. Studies on these systems will expand our understanding of the repertoire of small RNA regulators.
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Affiliation(s)
- Keith E Weaver
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069, USA.
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30
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Abstract
Recent genomic analyses revealed a surprisingly large number of toxin-antitoxin loci in free-living prokaryotes. The antitoxins are proteins or antisense RNAs that counteract the toxins. Two antisense RNA-regulated toxin-antitoxin gene families, hok/sok and ldr, are unrelated sequence-wise but have strikingly similar properties at the level of gene and RNA organization. Recently, two SOS-induced toxins were found to be regulated by RNA antitoxins. One such toxin, SymE, exhibits similarity with MazE antitoxin and, surprisingly, inhibits translation. Thus, it is possible that an ancestral antitoxin gene evolved into the present toxin gene (symE) whose translation is repressed by an RNA antitoxin (SymR).
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Affiliation(s)
- Kenn Gerdes
- Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, Newcastle NE2 4HH, UK.
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31
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Patel S, Weaver KE. Addiction toxin Fst has unique effects on chromosome segregation and cell division in Enterococcus faecalis and Bacillus subtilis. J Bacteriol 2006; 188:5374-84. [PMID: 16855226 PMCID: PMC1540048 DOI: 10.1128/jb.00513-06] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Fst toxin of the Enterococcus faecalis pAD1-encoded par addiction module functions intracellularly to kill plasmid-free segregants. Previous results had shown that Fst induction results in membrane permeabilization and cessation of macromolecular synthesis, but only after 45 min. Electron micrographs of toxin-induced cells showed no obvious membrane abnormalities but did reveal defects in nucleoid segregation and cell division, begging the question of which is the primary effect of Fst. To distinguish the possibilities, division septae and nucleoids were visualized simultaneously with fluorescent vancomycin and a variety of DNA stains. Results showed that division and segregation defects occurred in some cells within 15 min after induction. At these early time points, affected cells remained resistant to membrane-impermeant DNA stains, suggesting that loss of membrane integrity is a secondary effect caused by ongoing division and/or segregation defects. Fst-resistant mutants showed greater variability in cell length and formed multiple septal rings even in the absence of Fst. Fst induction was also toxic to Bacillus subtilis. In this species, Fst induction caused only minor division abnormalities, but all cells showed a condensation of the nucleoid, suggesting that effects on the structure of the chromosomal DNA might be paramount.
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Affiliation(s)
- S Patel
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57049, USA
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32
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Weaver KE, Ehli EA, Nelson JS, Patel S. Antisense RNA regulation by stable complex formation in the Enterococcus faecalis plasmid pAD1 par addiction system. J Bacteriol 2004; 186:6400-8. [PMID: 15375120 PMCID: PMC516608 DOI: 10.1128/jb.186.19.6400-6408.2004] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The par stability determinant, encoded by the Enterococcus faecalis plasmid pAD1, is the only antisense RNA regulated postsegregational killing system identified in gram-positive bacteria. Because of the unique organization of the par locus, the par antisense RNA, RNA II, binds to its target, RNA I, at relatively small, interspersed regions of complementarity. The results of this study suggest that, rather than targeting the antisense bound message for rapid degradation, as occurs in most other antisense RNA regulated systems, RNA I and RNA II form a relatively stable, presumably translationally inactive complex. The stability of the RNA I-RNA II complex would allow RNA I to persist in an untranslated state unless or until the encoding plasmid was lost. After plasmid loss, RNA II would be removed from the complex, allowing translational activation of RNA I. The mechanism of RNA I activation in vivo is unknown, but in vitro dissociation experiments suggest that active removal of RNA II, for example by a cellular RNase, may be required.
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Affiliation(s)
- Keith E Weaver
- Division of Basic Biomedical Sciences, School of Medicine, University of South Dakota, Vermillion, South Dakota 57069, USA.
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33
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Weaver KE, Weaver DM, Wells CL, Waters CM, Gardner ME, Ehli EA. Enterococcus faecalis plasmid pAD1-encoded Fst toxin affects membrane permeability and alters cellular responses to lantibiotics. J Bacteriol 2003; 185:2169-77. [PMID: 12644486 PMCID: PMC151501 DOI: 10.1128/jb.185.7.2169-2177.2003] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Fst is a peptide toxin encoded by the par toxin-antitoxin stability determinant of Enterococcus faecalis plasmid pAD1. Intracellular overproduction of Fst resulted in simultaneous inhibition of all cellular macromolecular synthesis concomitant with cell growth inhibition and compromised the integrity of the cell membrane. Cells did not lyse or noticeably leak intracellular contents but had specific defects in chromosome partitioning and cell division. Extracellular addition of synthetic Fst had no effect on cell growth. Spontaneous Fst-resistant mutants had a phenotype consistent with changes in membrane composition. Interestingly, overproduction of Fst sensitized cells to the lantibiotic nisin, and Fst-resistant mutants were cross-resistant to nisin and the pAD1-encoded cytolysin.
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Affiliation(s)
- Keith E Weaver
- Division of Basic Biomedical Sciences, School of Medicine, University of South Dakota, Vermillion, South Dakota 57069, USA.
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34
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Abstract
For a long time, RNA has been merely regarded as a molecule that can either function as a messenger (mRNA) or as part of the translational machinery (tRNA, rRNA). Meanwhile, it became clear that RNAs are versatile molecules that do not only play key roles in many important biological processes like splicing, editing, protein export and others, but can also--like enzymes--act catalytically. Two important aspects of RNA function--antisense-RNA control and RNA interference (RNAi)--are emphasized in this review. Antisense-RNA control functions in all three kingdoms of life--although the majority of examples are known from bacteria. In contrast, RNAi, gene silencing triggered by double-stranded RNA, the oldest and most ubiquitous antiviral system, is exclusively found in eukaryotes. Our current knowledge about occurrence, biological roles and mechanisms of action of antisense RNAs as well as the recent findings about involved genes/enzymes and the putative mechanism of RNAi are summarized. An interesting intersection between both regulatory mechanisms is briefly discussed.
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Affiliation(s)
- Sabine Brantl
- Institut für Molekularbiologie, Friedrich Schiller Univ. Jena, Winzerlaer Str. 10, D-07745 Jena, Germany.
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35
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Greenfield TJ, Franch T, Gerdes K, Weaver KE. Antisense RNA regulation of the par post-segregational killing system: structural analysis and mechanism of binding of the antisense RNA, RNAII and its target, RNAI. Mol Microbiol 2001; 42:527-37. [PMID: 11703673 DOI: 10.1046/j.1365-2958.2001.02663.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The par stability determinant of the Enterococcus faecalis plasmid pAD1 is the first antisense RNA regulated post-segregational killing system (PSK) identified in a Gram-positive organism. Par encodes two small, convergently transcribed RNAs, designated RNAI and RNAII, which are the toxin and antitoxin of the par PSK system respectively. RNAI encodes an open reading frame for a 33 amino acid toxin called Fst. Expression of fst is regulated post-transcriptionally by RNAII. RNAII interacts with RNAI by a unique antisense RNA mechanism involving binding at the 5' and 3' ends of both RNAs. Par RNA interaction requires a complementary transcriptional terminator stem-loop and a set of direct repeat sequences, DRa and DRb, located at the 5' end of both RNAs. The secondary structures of RNAI, RNAII and the RNAI-RNAII complex were analysed by partial digestion with Pb(II) and ribonucleases. Probing data for RNAI and RNAII are consistent with previously reported computer generated models, and also confirm that complementary direct repeat and terminator sequences are involved in the formation of the RNAI-RNAII complex. Mutant par RNAs were used to show that the binding reaction occurs in at least two steps. The first step is the formation of an initial kissing interaction between the transcriptional terminator stem-loops of both RNAs. The subsequent step(s) involves an initial pairing of the complementary direct repeat sequences followed by complete hybridization of the 5' nucleotides to stabilize the RNAI-RNAII complex.
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MESH Headings
- Amino Acid Sequence
- Base Sequence
- Binding Sites
- Binding, Competitive
- Enterococcus faecalis/genetics
- Gene Expression Regulation, Bacterial
- Molecular Sequence Data
- Mutation/genetics
- Nuclease Protection Assays
- Nucleic Acid Conformation
- Nucleic Acid Hybridization
- Open Reading Frames/genetics
- Plasmids/genetics
- RNA/chemistry
- RNA/genetics
- RNA/metabolism
- RNA, Antisense/chemistry
- RNA, Antisense/genetics
- RNA, Antisense/metabolism
- RNA, Bacterial/chemistry
- RNA, Bacterial/genetics
- RNA, Bacterial/metabolism
- RNA, Small Interfering
- Ribonucleases/metabolism
- Transcription, Genetic
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Affiliation(s)
- T J Greenfield
- Division of Basic Biomedical Sciences, School of Medicine, University of South Dakota, Vermillion, SD 57069, USA
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36
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Abstract
Bacterial plasmids deploy a diverse range of regulatory mechanisms to control expression of the functions they need to survive in the host population. Understanding of the mechanisms by which autoregulatory circuits control plasmid survival functions, in particular plasmid replication, has been advanced by recent studies. At a molecular level, structural understanding of how certain antisense RNAs control replication and stability functions is almost complete. Control circuits linking plasmid transfer functions to the status of the bacterial population have been dissected, uncovering a complex and hierarchical organisation. Coordinate or global regulation of plasmid replication, transfer and stable maintenance functions is becoming apparent across a range of plasmid families.
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Affiliation(s)
- L E Bingle
- School of Biosciences, University of Birmingham, Edgbaston, B15 2TT, Birmingham, UK
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37
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Kreikemeyer B, Boyle MD, Buttaro BA, Heinemann M, Podbielski A. Group A streptococcal growth phase-associated virulence factor regulation by a novel operon (Fas) with homologies to two-component-type regulators requires a small RNA molecule. Mol Microbiol 2001; 39:392-406. [PMID: 11136460 DOI: 10.1046/j.1365-2958.2001.02226.x] [Citation(s) in RCA: 163] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A novel growth phase-associated two-component-type regulator, Fas (fibronectin/fibrinogen binding/haemolytic activity/streptokinase regulator), of Streptococcus pyogenes was identified in the M1 genome sequence, based on homologies to the histidine protein kinase (HPK) and response regulator (RR) part of the Staphylococcus aureus Agr and Streptococcus pneumoniae Com quorum-sensing systems. The fas operon, present in all 12 tested M serotypes, was transcribed as polycystronic message (fasBCA) and contained genes encoding two potential HPKs (FasB and FasC) and one RR (FasA). Downstream of fasBCA, we identified a small 300 nucleotide monocistronic transcript, designated fasX, that did not appear to encode true peptide sequences. Measurements of luciferase promoter fusions revealed a growth phase-associated transcription of fasBCA and fasX, with peak activities during the late exponential phase. Insertional mutagenesis disrupting fasBCA and fasA led to a phenotype similar to agr-null mutations in S. aureus, with prolonged expression of extracellular matrix protein-binding adhesins and reduced expression of secreted virulence factors such as streptokinase and streptolysin S. In addition, fasX transcription was dependent on the RR FasA; however, deletion mutagenesis of fasX resulted in a similar phenotype to that of the fasBCA or fasA mutants. Complementation of the fasX deletion mutant, with the fasX gene expressed in trans from a plasmid, restored the wild-type fasBCA regulation pattern. This strongly suggested that fasX, a putative non-translated RNA, is the main effector molecule of the fas regulon. However, using spent culture supernatants from wild-type and fas mutant strains, we were not able to show an influence on the logarithmic growth phase expression of fas and dependent genes. Thus, despite structural and functional similarities between fas and agr, to date the fas operon appears not to be involved in group A streptococcal (GAS) quorum-sensing regulation.
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Affiliation(s)
- B Kreikemeyer
- Department of Medical Microbiology and Hygiene, University Hospital Ulm, Robert-Koch-Str. 8, D-89081 Ulm, Germany
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