title: Regulation of traJ transcription in the Salmonella virulence plasmid by strand-specific DNA adenine hemimethylation.
abstract: The traJ gene of the virulence plasmid of Salmonella enterica serovar Typhimurium (pSLT) encodes a transcriptional activator of the transfer operon. The leucine-responsive regulatory protein (Lrp) is an activator of traJ transcription. The upstream-activating-sequence of the pSLT traJ promoter contains two Lrp binding sites (LRP-1 and LRP-2), both necessary for transcriptional activation. The promoter-proximal site (LRP-2) contains a GATC site (GATC-II) whose methylation state affects Lrp binding: GATC-II methylation in both DNA strands decreases the affinity of Lrp for the LRP-2 site, while efficient Lrp binding occurs to a non-methylated GATC-II site. The effect of GATC-II hemimethylation on Lrp binding is strand-specific: methylation of the traJ non-coding strand permits formation of the major Lrp-DNA retardation complex, but methylation of the coding strand does not. This asymmetry supports a model in which passage of the replication fork may permit Lrp-mediated activation of conjugal transfer in one daughter plasmid molecule but not in the other. A remarkable trait of this regulatory design is that hemimethylation of a single GATC site can generate distinct epigenetic signals in otherwise identical plasmid DNA molecules.
authors.affiliation: Departamento de Genética, Facultad de Biología, Universidad de Sevilla, 41080 Sevilla, Spain.
authors.forename: Eva M
authors.initials: EM
authors.lastname: Camacho
authors.forename: Josep
authors.initials: J
authors.lastname: Casadesús
mesh_terms: D000225:Adenine / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D019175:DNA Methylation; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009876:Operon; D010957:Plasmids / Q000235:genetics / Q000378:metabolism*; D012486:Salmonella typhimurium / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity*; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific) / Q000378:metabolism; D014158:Transcription, Genetic; D014774:Virulence
chemical_list: D001425:Bacterial Outer Membrane Proteins; D004269:DNA, Bacterial; C041427:TraJ protein, bacteria; C058693:Dam methyltransferase; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); D000225:Adenine