Regulation of conjugal transfer by Lrp and Dam methylation in plasmid R100.

Conjugal transfer of the F-like plasmid R100 occurs at higher frequencies in the absence of DNA adenine methylation. Lower levels of R100-encoded FinP RNA were found in a Dam host, suggesting that Dam methylation regulates FinP RNA synthesis. Lack of the leucine-responsive regulatory protein (Lrp) causes a decrease in R100 plasmid transfer, indicating that Lrp is an activator of R100-mediated conjugation. Hence, host-encoded regulators previously described for the Salmonella virulence plasmid (pSLT) seem to play analogous roles in R100. Repression of conjugal transfer in rich medium is an additional trait shared by R100 and pSLT. DNA sequence comparisons in regulatory loci support the view that R100 and pSLT are closely related.