THE CONTROL REGION OF THE PDU COB REGULON IN SALMONELLA-TYPHIMURIUM/

The pdu operon encodes proteins for the catabolism of 1,2-propanediol; the nearby cab operon encodes enzymes for the biosynthesis of adenosy l-cobalamin (vitamin B-12), a cofactor required for the use of propane diol. These operons are transcribed divergently from distinct promoter s separated by several kilobases. The regulation of the two operons is tightly integrated in that both require the positive activator protei n PocR and both are subject to global control by the Crp and ArcA prot eins. We have determined the DNA nucleotide sequences of the promoter- proximal portion of the pdu operon and the region between the pda and cab operons. Four open reading frames have been identified, pduB, pduA , pduF, and pocR. The pduA and pduB genes are the first two genes of t he pdu operon (transcribed clockwise). The pduA gene encodes a hydroph obic protein with 56% amino acid identity to a 10.9-kDa protein which serves as a component of the carboxysomes of several photosynthetic ba cteria. The pduF gene encodes a hydrophobic protein with a strong simi larity to the GlpF protein of Escherichia coil, which facilitates the diffusion of glycerol. The N-terminal end of the PduF protein includes a moth for a membrane lipoprotein-lipid attachment site as well as a motif characteristic of the MIP (major intrinsic protein) family of tr ansmembrane channel proteins. We presume that the PduF protein facilit ates the diffusion of propanediol. The pocR gene encodes the positive regulatory protein of the cab and pdu operons and shares the helix-tur n-helix DNA binding motif of the AraC family of regulatory proteins. T he mutations cobR4 and cobR58 cause constitutive, pocR-independent exp ression of the cab operon under both aerobic and anaerobic conditions. Evidence that each mutation is a deletion creating a new promoter nea r the normal promoter site of the cab operon is presented.