Conjugal transfer of the virulence plasmid of Salmonella enterica is regulated by the leucine-responsive regulatory protein and DNA adenine methylation.
Host-encoded functions that regulate the transfer operon (tra) in the virulence plasmid of Salmonella enterica (pSLT) were identified with a genetic screen. Mutations that decreased tra operon expression mapped in the lrp gene, which encodes the leucine-responsive regulatory protein (Lrp). Reduced tra operon expression in an Lrp- background is caused by lowered transcription of the traJ gene, which encodes a transcriptional activator of the tra operon. Gel retardation assays indicated that Lrp binds a DNA region upstream of the traJ promoter. Deletion of the Lrp binding site resulted in lowered and Lrp-independent traJ transcription. Conjugal transfer of pSLT decreased 50-fold in a Lrp- background. When a FinO- derivative of pSLT was used, conjugal transfer from an Lrp- donor decreased 1000-fold. Mutations that derepressed tra operon expression mapped in dam, the gene encoding Dam methyltransferase. Expression of the tra operon and conjugal transfer remain repressed in an Lrp- Dam- background. These observations support the model that Lrp acts as a conjugation activator by promoting traJ transcription, whereas Dam methylation acts as a conjugation repressor by activating FinP RNA synthesis. This dual control of conjugal transfer may also operate in other F-like plasmids such as F and R100.
Camacho
Eva M
EM
Department of Genetics, School of Biology, University of Seville, Apartado 1095, 41080 Seville, Spain.
Casadesús
Josep
J
D000225:Adenine / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins; D003227:Conjugation, Genetic / Q000502:physiology*; D019175:DNA Methylation; D004268:DNA-Binding Proteins / Q000502:physiology*; D005144:F Factor / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D051756:Leucine-Responsive Regulatory Protein; D009876:Operon; D010957:Plasmids / Q000235:genetics; D019779:Salmonella enterica / Q000235:genetics* / Q000472:pathogenicity; D014157:Transcription Factors; D014158:Transcription, Genetic; D014774:Virulence; D001616:beta-Galactosidase / Q000378:metabolism
D001425:Bacterial Outer Membrane Proteins; D004268:DNA-Binding Proteins; C041427:TraJ protein, bacteria; D014157:Transcription Factors; D051756:Leucine-Responsive Regulatory Protein; D001616:beta-Galactosidase; D000225:Adenine