J. Bacteriol., 04 1996, 2196-2203, Vol 178, No. 8
Copyright © 1996, American Society for Microbiology

In vitro analysis of the interactions between the PocR regulatory protein and the promoter region of the cobalamin biosynthetic (cob) operon of Salmonella typhimurium LT2

MR Rondon and JC Escalante-Semerena
Department of Bacteriology, University of Wisconsin-Madison 53706, USA.

The PocR protein of Salmonella typhimurium LT2 was overexpressed and used to demonstrate in vitro that it specifically binds to the cobalamin biosynthetic operon (cob) promoter region. Evidence is presented to show that PocR DNA-binding activity in vitro is regulated by the effector molecule 1,2-propanediol. Deletion analysis of the cob promoter (Pcob) suggested that two regions upstream of the promoter are needed for optimal activation of Pcob by PocR in vivo. DNase I footprinting experiments demonstrated that PocR binds to two sites within Pcob. The transcription initiation site of cob mRNA in response to 1,2-propanediol was identified and shown to be different from the one reported for transcription initiation under anoxic conditions in the absence of 1,2-propanediol.

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