5 PROMOTERS INTEGRATE CONTROL OF THE COB PDU REGULON IN SALMONELLA-TYPHIMURIUM/

Propanediol is degraded by a B-12-dependent pathway in Salmonella typh imurium. The enzymes for this pathway are encoded in a small region (m inute 41) that includes the pdu operon (controlling B-12-dependent deg radation of propanediol) and the divergent cob operon (controlling syn thesis of cobalamin, B-12), Expression of both operons is induced by p ropanediol and globally controlled by the ArcA and Crp systems, The re gion between the two operons encodes two proteins, PduF, a transporter of propanediol, and PocR, which mediates the induction of the regulon by propanediol, Insertion mutations between the pdu and cob operons h ave been characterized, and their exact positions have been correlated with mutant phenotypes, The region includes five promoters, four of w hich are controlled by the PocR protein and induced by propanediol, Th e cob and pdu operons each have one regulated promoter; the pduF gene is expressed from two regulated promoters (PI and P2), The P1 and P2 t ranscripts extend beyond pduF to include the pocR gene; thus the PocR protein autoregulates its expression from these promoters, The fifth p romoter, P-Poc, is adjacent to the pocR gene and associated with a Crp binding site, We suggest that all global control of the regulon is ex erted by regulating the level of PocR protein at the P1, P2, and P-Poc promoters, A putative binding site for the PocR protein has been iden tified by computer analysis, Eight close matches to this proposed site were found in regions near the four promoters known to be regulated b y PocR protein: P-Pdu, P1, P2, and P-Cob, A three state model is propo sed in which the regulon uses all five of its promoters to control exp ression.