1
|
Mehlhoff JD, Ostermeier M. Genes Vary Greatly in Their Propensity for Collateral Fitness Effects of Mutations. Mol Biol Evol 2023; 40:7043719. [PMID: 36798991 PMCID: PMC9999109 DOI: 10.1093/molbev/msad038] [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: 10/24/2022] [Revised: 01/18/2023] [Accepted: 02/13/2023] [Indexed: 02/18/2023] Open
Abstract
Mutations can have deleterious fitness effects when they decrease protein specific activity or decrease active protein abundance. Mutations will also be deleterious when they cause misfolding or misinteractions that are toxic to the cell (i.e., independent of whether the mutations affect specific activity and abundance). The extent to which protein evolution is shaped by these and other collateral fitness effects is unclear in part because little is known of their frequency and magnitude. Using deep mutational scanning (DMS), we previously found at least 42% of missense mutations in the TEM-1 β-lactamase antibiotic resistance gene cause deleterious collateral fitness effects. Here, we used DMS to comprehensively determine the collateral fitness effects of missense mutations in three genes encoding the antibiotic resistance proteins New Delhi metallo-β-lactamase (NDM-1), chloramphenicol acetyltransferase I (CAT-I), and 2″-aminoglycoside nucleotidyltransferase (AadB). AadB (20%), CAT-I (0.9%), and NDM-1 (0.2%) were less susceptible to deleterious collateral fitness effects than TEM-1 (42%) indicating that genes have different propensities for these effects. As was observed with TEM-1, all the studied deleterious aadB mutants increased aggregation. However, aggregation did not correlate with collateral fitness effects for many of the deleterious mutants of CAT-I and NDM-1. Select deleterious mutants caused unexpected phenotypes to emerge. The introduction of internal start codons in CAT-1 caused loss of the episome and a mutation in aadB made its cognate antibiotic essential for growth. Our study illustrates how the complexity of the cell provides a rich environment for collateral fitness effects and new phenotypes to emerge.
Collapse
Affiliation(s)
- Jacob D Mehlhoff
- Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, MD
| | - Marc Ostermeier
- Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, MD
| |
Collapse
|
2
|
DNA Methylation in Prokaryotes. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2022; 1389:21-43. [DOI: 10.1007/978-3-031-11454-0_2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
|
3
|
Bruneaux M, Kronholm I, Ashrafi R, Ketola T. Roles of adenine methylation and genetic mutations in adaptation to different temperatures in Serratia marcescens. Epigenetics 2021; 17:861-881. [PMID: 34519613 DOI: 10.1080/15592294.2021.1966215] [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: 10/20/2022] Open
Abstract
Epigenetic modifications can contribute to adaptation, but the relative contributions of genetic and epigenetic variation are unknown. Previous studies on the role of epigenetic changes in adaptation in eukaryotes have nearly exclusively focused on cytosine methylation (m5C), while prokaryotes exhibit a richer system of methyltransferases targetting adenines (m6A) or cytosines (m4C, m5C). DNA methylation in prokaryotes has many roles, but its potential role in adaptation still needs further investigation. We collected phenotypic, genetic, and epigenetic data using single molecule real-time sequencing of clones of the bacterium Serratia marcescens that had undergone experimental evolution in contrasting temperatures to investigate the relationship between environment and genetic, epigenetic, and phenotypic changes. The genomic distribution of GATC motifs, which were the main target for m6A methylation, and of variable m6A epiloci pointed to a potential link between m6A methylation and regulation of gene expression in S. marcescens. Evolved strains, while genetically homogeneous, exhibited many polymorphic m6A epiloci. There was no strong support for a genetic control of methylation changes in our experiment, and no clear evidence of parallel environmentally induced or environmentally selected methylation changes at specific epiloci was found. Both genetic and epigenetic variants were associated with some phenotypic traits. Overall, our results suggest that both genetic and adenine methylation changes have the potential to contribute to phenotypic adaptation in S. marcescens, but that any environmentally induced epigenetic change occurring in our experiment would probably have been quite labile.
Collapse
Affiliation(s)
- Matthieu Bruneaux
- Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland
| | - Ilkka Kronholm
- Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland
| | - Roghaieh Ashrafi
- Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland
| | - Tarmo Ketola
- Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland
| |
Collapse
|
4
|
García-Pastor L, Sánchez-Romero MA, Jakomin M, Puerta-Fernández E, Casadesús J. Regulation of bistability in the std fimbrial operon of Salmonella enterica by DNA adenine methylation and transcription factors HdfR, StdE and StdF. Nucleic Acids Res 2019; 47:7929-7941. [PMID: 31216025 PMCID: PMC6735912 DOI: 10.1093/nar/gkz530] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 05/31/2019] [Accepted: 06/05/2019] [Indexed: 01/16/2023] Open
Abstract
Bistable expression of the Salmonella enterica std operon is controlled by an AND logic gate involving three transcriptional activators: the LysR-type factor HdfR and the StdE and StdF regulators encoded by the std operon itself. StdE activates transcription of the hdfR gene, and StdF activates std transcription together with HdfR. Binding of HdfR upstream of the std promoter is hindered by methylation of GATC sites located within the upstream activating sequence (UAS). Epigenetic control by Dam methylation thus antagonizes formation of the StdE-StdF-HdfR loop and tilts the std switch toward the StdOFF state. In turn, HdfR binding hinders methylation of the UAS, permitting activation of the StdE-StdF-HdfR loop and concomitant formation of StdON cells. Bistability is thus the outcome of competition between DNA adenine methylation and the StdE-StdF-HdfR activator loop.
Collapse
Affiliation(s)
- Lucía García-Pastor
- Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Apartado 1095, 41080 Sevilla, Spain
| | - María A Sánchez-Romero
- Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Apartado 1095, 41080 Sevilla, Spain
| | - Marcello Jakomin
- Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Apartado 1095, 41080 Sevilla, Spain
| | - Elena Puerta-Fernández
- Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Apartado 1095, 41080 Sevilla, Spain
- Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS, CSIC), Avda. Reina Mercedes, 10, 41012 Sevilla, Spain
| | - Josep Casadesús
- Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Apartado 1095, 41080 Sevilla, Spain
| |
Collapse
|
5
|
Salmonella enterica Serovar Typhi Lipopolysaccharide O-Antigen Modification Impact on Serum Resistance and Antibody Recognition. Infect Immun 2017; 85:IAI.01021-16. [PMID: 28167670 PMCID: PMC5364305 DOI: 10.1128/iai.01021-16] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2016] [Accepted: 01/30/2017] [Indexed: 11/20/2022] Open
Abstract
Salmonella enterica serovar Typhi is a human-restricted Gram-negative bacterial pathogen responsible for causing an estimated 27 million cases of typhoid fever annually, leading to 217,000 deaths, and current vaccines do not offer full protection. The O-antigen side chain of the lipopolysaccharide is an immunodominant antigen, can define host-pathogen interactions, and is under consideration as a vaccine target for some Gram-negative species. The composition of the O-antigen can be modified by the activity of glycosyltransferase (gtr) operons acquired by horizontal gene transfer. Here we investigate the role of two gtr operons that we identified in the S. Typhi genome. Strains were engineered to express specific gtr operons. Full chemical analysis of the O-antigens of these strains identified gtr-dependent glucosylation and acetylation. The glucosylated form of the O-antigen mediated enhanced survival in human serum and decreased complement binding. A single nucleotide deviation from an epigenetic phase variation signature sequence rendered the expression of this glucosylating gtr operon uniform in the population. In contrast, the expression of the acetylating gtrC gene is controlled by epigenetic phase variation. Acetylation did not affect serum survival, but phase variation can be an immune evasion mechanism, and thus, this modification may contribute to persistence in a host. In murine immunization studies, both O-antigen modifications were generally immunodominant. Our results emphasize that natural O-antigen modifications should be taken into consideration when assessing responses to vaccines, especially O-antigen-based vaccines, and that the Salmonellagtr repertoire may confound the protective efficacy of broad-ranging Salmonella lipopolysaccharide conjugate vaccines.
Collapse
|
6
|
Casadesús J. Bacterial DNA Methylation and Methylomes. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 945:35-61. [PMID: 27826834 DOI: 10.1007/978-3-319-43624-1_3] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
Formation of C5-methylcytosine, N4-methylcytosine, and N6-methyladenine in bacterial genomes is postreplicative and involves transfer of a methyl group from S-adenosyl-methionine to a base embedded in a specific DNA sequence context. Most bacterial DNA methyltransferases belong to restriction-modification systems; in addition, "solitary" or "orphan" DNA methyltransferases are frequently found in the genomes of bacteria and phage. Base methylation can affect the interaction of DNA-binding proteins with their cognate sites, either by a direct effect (e.g., steric hindrance) or by changes in DNA topology. In both Alphaproteobacteria and Gammaproteobacteria, the roles of DNA base methylation are especially well known for N6-methyladenine, including control of chromosome replication, nucleoid segregation, postreplicative correction of DNA mismatches, cell cycle-coupled transcription, formation of bacterial cell lineages, and regulation of bacterial virulence. Technical procedures that permit genome-wide analysis of DNA methylation are nowadays expanding our knowledge of the extent, evolution, and physiological significance of bacterial DNA methylation.
Collapse
Affiliation(s)
- Josep Casadesús
- Departamento de Genética, Universidad de Sevilla, Apartado 1095, Seville, 41080, Spain.
| |
Collapse
|
7
|
Abstract
The DNA of Escherichia coli contains 19,120 6-methyladenines and 12,045 5-methylcytosines in addition to the four regular bases, and these are formed by the postreplicative action of three DNA methyltransferases. The majority of the methylated bases are formed by the Dam and Dcm methyltransferases encoded by the dam (DNA adenine methyltransferase) and dcm (DNA cytosine methyltransferase) genes. Although not essential, Dam methylation is important for strand discrimination during the repair of replication errors, controlling the frequency of initiation of chromosome replication at oriC, and the regulation of transcription initiation at promoters containing GATC sequences. In contrast, there is no known function for Dcm methylation, although Dcm recognition sites constitute sequence motifs for Very Short Patch repair of T/G base mismatches. In certain bacteria (e.g., Vibrio cholerae, Caulobacter crescentus) adenine methylation is essential, and, in C. crescentus, it is important for temporal gene expression, which, in turn, is required for coordinating chromosome initiation, replication, and division. In practical terms, Dam and Dcm methylation can inhibit restriction enzyme cleavage, decrease transformation frequency in certain bacteria, and decrease the stability of short direct repeats and are necessary for site-directed mutagenesis and to probe eukaryotic structure and function.
Collapse
|
8
|
Abstract
Contrary to the traditional view that bacterial populations are clonal, single-cell analysis reveals that phenotypic heterogeneity is common in bacteria. Formation of distinct bacterial lineages appears to be frequent during adaptation to harsh environments, including the colonization of animals by bacterial pathogens. Formation of bacterial subpopulations is often controlled by epigenetic mechanisms that generate inheritable phenotypic diversity without altering the DNA sequence. Such mechanisms are diverse, ranging from relatively simple feedback loops to complex self-perpetuating DNA methylation patterns.
Collapse
Affiliation(s)
- Josep Casadesús
- Departamento de Genética, Facultad de Biología, Universidad de Sevilla, 41080 Seville, Spain.
| | - David A Low
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, California 93106.
| |
Collapse
|
9
|
Abstract
The activities of DNA methyltransferases are important for a variety of cellular functions in bacteria. In this study, we developed a modified high-throughput technique called methyl homopolymer tail mediated sequencing (methyl HTM-seq) to identify the undermethylated sites in the Vibrio cholerae genome for the two DNA methyltransferases, Dam, an adenine methyltransferase, and VchM, a cytosine methyltransferase, during growth in rich medium in vitro. Many of the undermethylated sites occurred in intergenic regions, and for most of these sites, we identified the transcription factors responsible for undermethylation. This confirmed the presence of previously hypothesized DNA-protein interactions for these transcription factors and provided insight into the biological state of these cells during growth in vitro. DNA adenine methylation has previously been shown to mediate heritable epigenetic switches in gene regulation. However, none of the undermethylated Dam sites tested showed evidence of regulation by this mechanism. This study is the first to identify undermethylated adenines and cytosines genomewide in a bacterium using second-generation sequencing technology.
Collapse
|
10
|
Gonzalez D, Collier J. DNA methylation by CcrM activates the transcription of two genes required for the division of Caulobacter crescentus. Mol Microbiol 2013; 88:203-18. [PMID: 23480529 PMCID: PMC3708114 DOI: 10.1111/mmi.12180] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/07/2013] [Indexed: 11/29/2022]
Abstract
DNA methylation regulates many processes, including gene expression, by superimposing secondary information on DNA sequences. The conserved CcrM enzyme, which methylates adenines in GANTC sequences, is essential to the viability of several Alphaproteobacteria. In this study, we find that Caulobacter crescentus cells lacking the CcrM enzyme accumulate low levels of the two conserved FtsZ and MipZ proteins, leading to a severe defect in cell division. This defect can be compensated by the expression of the ftsZ gene from an inducible promoter or by spontaneous suppressor mutations that promote FtsZ accumulation. We show that CcrM promotes the transcription of the ftsZ and mipZ genes and that the ftsZ and mipZ promoter regions contain a conserved CGACTC motif that is critical to their activities and to their regulation by CcrM. In addition, our results suggest that the ftsZ promoter has the lowest activity when the CGACTC motif is non-methylated, an intermediate activity when it is hemi-methylated and the highest activity when it is fully methylated. The regulation of ftsZ expression by DNA methylation may explain why CcrM is essential in a subset of Alphaproteobacteria.
Collapse
Affiliation(s)
- Diego Gonzalez
- Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, Quartier UNIL/Sorge, Lausanne, CH 1015, Switzerland
| | | |
Collapse
|
11
|
Pollak AJ, Reich NO. Proximal recognition sites facilitate intrasite hopping by DNA adenine methyltransferase: mechanistic exploration of epigenetic gene regulation. J Biol Chem 2012; 287:22873-81. [PMID: 22570478 DOI: 10.1074/jbc.m111.332502] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The methylation of adenine in palindromic 5'-GATC-3' sites by Escherichia coli Dam supports diverse roles, including the essential regulation of virulence genes in several human pathogens. As a result of a unique hopping mechanism, Dam methylates both strands of the same site prior to fully dissociating from the DNA, a process referred to as intrasite processivity. The application of a DpnI restriction endonuclease-based assay allowed the direct interrogation of this mechanism with a variety of DNA substrates. Intrasite processivity is disrupted when the DNA flanking a single GATC site is longer than 400 bp on either side. Interestingly, the introduction of a second GATC site within this flanking DNA reinstates intrasite methylation of both sites. Our results show that intrasite methylation occurs only when GATC sites are clustered, as is found in gene segments both known and postulated to undergo in vivo epigenetic regulation by Dam methylation. We propose a model for intrasite methylation in which Dam bound to flanking DNA is an obligate intermediate. Our results provide insights into how intrasite processivity, which appears to be context-dependent, may contribute to the diverse biological roles that are carried out by Dam.
Collapse
Affiliation(s)
- Adam J Pollak
- Department of Chemistry and Biochemistry University of California, Santa Barbara, California 93106-9510, USA
| | | |
Collapse
|
12
|
Brunet YR, Bernard CS, Gavioli M, Lloubès R, Cascales E. An epigenetic switch involving overlapping fur and DNA methylation optimizes expression of a type VI secretion gene cluster. PLoS Genet 2011; 7:e1002205. [PMID: 21829382 PMCID: PMC3145626 DOI: 10.1371/journal.pgen.1002205] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Accepted: 06/08/2011] [Indexed: 11/18/2022] Open
Abstract
Type VI secretion systems (T6SS) are macromolecular machines of the cell envelope of Gram-negative bacteria responsible for bacterial killing and/or virulence towards different host cells. Here, we characterized the regulatory mechanism underlying expression of the enteroagregative Escherichia coli sci1 T6SS gene cluster. We identified Fur as the main regulator of the sci1 cluster. A detailed analysis of the promoter region showed the presence of three GATC motifs, which are target of the DNA adenine methylase Dam. Using a combination of reporter fusion, gel shift, and in vivo and in vitro Dam methylation assays, we dissected the regulatory role of Fur and Dam-dependent methylation. We showed that the sci1 gene cluster expression is under the control of an epigenetic switch depending on methylation: fur binding prevents methylation of a GATC motif, whereas methylation at this specific site decreases the affinity of Fur for its binding box. A model is proposed in which the sci1 promoter is regulated by iron availability, adenine methylation, and DNA replication. DNA methylation plays an important role in the regulation of genes involved in assembly of cell surface adhesins or appendages. Methylation at a GATC motif by the Dam methylase influences binding of transcriptional regulators, leading to variation in the gene expression pattern. In several cases, this may lead to different cell subpopulations allowing a rapid adaptation to varying environments. In this work, we uncover the regulatory mechanism controlling expression of the sci1 Type VI secretion gene cluster in entero-aggregative Escherichia coli, which encodes a structure required for inter-bacterial interaction. We showed that this gene cluster is repressed by Fur in iron-replete conditions and that Fur binding on the promoter prevents methylation of a GATC motif. In iron-limited conditions, Fur is relieved from the promoter allowing expression of the gene cluster and methylation of the GATC motif. Methylation prevents de novo Fur binding allowing constitutive expression. Our findings support a model in which the expression of the Type VI secretion gene cluster is regulated by a non-stochastic epigenetic switch: switch from the OFF to ON phases depends on iron availability whereas the ON to OFF switch depends on DNA replication and competition between Dam-dependent methylation and Fur binding.
Collapse
Affiliation(s)
- Yannick R. Brunet
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires, CNRS – UPR 9027, Institut de Microbiologie de la Méditerranée, Aix-Marseille Université, Marseille, France
| | - Christophe S. Bernard
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires, CNRS – UPR 9027, Institut de Microbiologie de la Méditerranée, Aix-Marseille Université, Marseille, France
| | - Marthe Gavioli
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires, CNRS – UPR 9027, Institut de Microbiologie de la Méditerranée, Aix-Marseille Université, Marseille, France
| | - Roland Lloubès
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires, CNRS – UPR 9027, Institut de Microbiologie de la Méditerranée, Aix-Marseille Université, Marseille, France
| | - Eric Cascales
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires, CNRS – UPR 9027, Institut de Microbiologie de la Méditerranée, Aix-Marseille Université, Marseille, France
- * E-mail:
| |
Collapse
|
13
|
Epigenetic switches: can infidelity govern fate in microbes? Curr Opin Microbiol 2011; 14:212-7. [PMID: 21496764 DOI: 10.1016/j.mib.2010.12.004] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2010] [Revised: 12/09/2010] [Accepted: 12/10/2010] [Indexed: 11/24/2022]
Abstract
Unicellular organisms are constantly subject to sudden changes in environment. Here, we describe recent progress in understanding how epigenetic mechanisms can generate differentiation within genetically identical single cells of a clonal population. Such intrinsic phenotypic heterogeneity within a population may be considered as a bet-hedging strategy in fluctuating environments. One aspect we highlight is how transient errors in information transfer, be it errors in transcription or translation, or alternatives in protein folding, can influence the quantity and the quality of the resulting proteins, and therefore, contribute to genetic noise within individual cells. These stochastic events can provide the impetus for heritable phenotypic change in bistable epigenetic regulatory networks that are susceptible to noise and proteins capable of dominant variant conformations.
Collapse
|
14
|
Phase variation: how to create and coordinate population diversity. Curr Opin Microbiol 2011; 14:205-11. [DOI: 10.1016/j.mib.2011.01.002] [Citation(s) in RCA: 119] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2010] [Revised: 01/06/2011] [Accepted: 01/07/2011] [Indexed: 12/26/2022]
|
15
|
Broadbent SE, Davies MR, van der Woude MW. Phase variation controls expression of Salmonella lipopolysaccharide modification genes by a DNA methylation-dependent mechanism. Mol Microbiol 2010; 77:337-53. [PMID: 20487280 PMCID: PMC2909390 DOI: 10.1111/j.1365-2958.2010.07203.x] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/03/2010] [Indexed: 02/06/2023]
Abstract
The O-antigen of Salmonella lipopolysaccharide is a major antigenic determinant and its chemical composition forms the basis for Salmonella serotyping. Modifications of the O-antigen that can affect the serotype include those carried out by the products of glycosyltransferase operons (gtr), which are present on specific Salmonella and phage genomes. Here we show that expression of the gtr genes encoded by phage P22 that confers the O1 serotype is under the control of phase variation. This phase variation occurs by a novel epigenetic mechanism requiring OxyR in conjunction with the DNA methyltransferase Dam. OxyR is an activator or a repressor of the system depending on which of its two binding sites in the gtr regulatory region is occupied. Binding is decreased by methylation at Dam target sequences in either site, and this confers heritability of the expression state to the system. Most Salmonella gtr operons share the key regulatory elements that are identified here as essential for this epigenetic phase variation.
Collapse
Affiliation(s)
- S E Broadbent
- Centre for Immunology and Infection, Hull York Medical School and the Department of Biology, University of YorkYork, UK
| | - M R Davies
- Centre for Immunology and Infection, Hull York Medical School and the Department of Biology, University of YorkYork, UK
| | - M W van der Woude
- Centre for Immunology and Infection, Hull York Medical School and the Department of Biology, University of YorkYork, UK
| |
Collapse
|