THE POC LOCUS IS REQUIRED FOR 1,2-PROPANEDIOL-DEPENDENT TRANSCRIPTIONOF THE COBALAMIN BIOSYNTHETIC (COB) AND PROPANEDIOL UTILIZATION (PDU)GENES OF SALMONELLA-TYPHIMURIUM

In this communication we present evidence that indicates that 1,2-prop anediol (1,2-PDL) is a positive effector of the transcription of the c obalamin (vitamin B-12) biosynthetic (cob) operon and of the 1,2-PDL u tilization (pdu) genes. The stimulatory effects of 1,2-PDL were demons trated using Mu d-lac transcriptional fusions to cob and pdu. Signific antly increased levels of transcription of the cob and pdu operon fusi ons were measured in cultures grown under both anoxic and highly aerat ed conditions when 1,2-PDL was present in the culture medium. We have isolated mutants that carry lesions that render both pdu and cob trans cription unresponsive to 1,2-PDL. These mutations were mapped to the r egion between cob and pdu (41 min), and they define the poc locus PDL and cobalamin). The poc locus is required for the positive regulatory effects of 1,2-PDL to be exerted. Complementation of Poc function was achieved in trans by an F' plasmid carrying the poc+ locus, suggesting that at least one diffusible product regulates the expression of cob and pdu in S. typhimurium.