Identification of operators and promoters that control SXT conjugative transfer

Transfer of SXT, a Vibrio cholerae-derived integrating conjugative element that encodes multiple antibiotic resistance genes, is repressed by SetR, a lambda(434) cI-related repressor. Here we identify divergent promoters between s086 and setR that drive expression of the regulators of SXT transfer. One transcript encodes the activators of transfer, setC and setD. The second transcript codes for SetR and, like the cl transcript of lambda, is leaderless. SetR binds to four operators located between setR and s086; the locations and relative affinities of these sites suggest a model for regulation of SXT transfer.