Regulation of Vibrio cholerae genes required for acid tolerance by a member of the "ToxR-like" family of transcriptional regulators

The ability of the intestinal pathogen I Vibrio cholerae to undergo an adap tive stress response, known as the acid tolerance response (ATR), was previ ously shown to enhance virulence. An essential component of the ATR is CadA -mediated lysine decarboxylation. CadA is encoded by the acid- and infectio n-induced gene cadA, Herein, cad4 is shown to be the second gene in an oper on with cadB, encoding a lysine/cadaverine antiporter. cadC, which is 5' of cadB, encodes an acid-responsive, positive transcriptional regulator of ca dBA. Unlike in Escherichia coli, V. cholerae cadB and cadA are also transcr ibed monocistronitally. Of note, bicistronic cadBA is transcribed at low co nstitutive levels in an acid- and CadC-independent manner. CadC represents a new member of the "ToxR-like" family of transcriptional regulators in V., cholerae and, in addition, exhibits extensive amino acid and functional si milarity to E. coli CadC, The amino-terminal, putative DNA binding domains of ToxR and CadC are highly conserved, as are the putative promoter element s recognized by these transcription factors.