CHARACTERIZATION OF A CO-RESPONSIVE TRANSCRIPTIONAL ACTIVATOR FROM RHODOSPIRILLUM-RUBRUM

In Rhodospirillum rubrum, CO induces the expression of at least two tr anscripts that encode an enzyme system for CO oxidation. This regulon is positively regulated by CooA, which is a member of the cAMP recepto r protein family of transcriptional regulators. The transcriptional st art site of one of the transcripts (cooFSCTJ) has been identified by p rimer extension, The ability of CooA to bind to this promoter in vitro was characterized with DNase I footprinting experiments using extract s of a CooA-overproducing strain. CooA- and CO-dependent protection wa s observed for a region with a-fold symmetry (5'-TGTCA-N-6-CGACA) that is highly similar to the consensus core motifs recognized by cAMP rec eptor protein/FNR family. In vivo analysis in a heterologous backgroun d indicates that CooA is sufficient for CO-dependent expression, impli cating it as the likely CO sensor.