TRANSCRIPTIONAL CONTROL OF GENES ENCODING CS1 PILI - NEGATIVE REGULATION BY A SILENCER AND POSITIVE REGULATION BY RNS

The adherence of enterotoxigenic Escherichia coli (ETEC) to the human small intestine is an important early event in infection, Attachment i s thought to be mediated by proteinaceous structures called pill, We h ave investigated the regulation of expression of the genes encoding CS 1 pill found on human ETEC strains and find that there are at least th ree promoters, P1 and P2, upstream of the coo genes, and P3, downstrea m of the start of cooB translation. We identified a silencer of transc ription which extends over several hundred bases overlapping the cooB open reading frame, This silencer is dependent on the promoter and/or upstream region for its negative effect, The DNA binding protein H-NS is a repressor of coo transcription that acts in the same region as th e silencer, so it is possible that H-NS is involved in this silencing, Rns, a member of the AraC family, positively regulates transcription of the coo operon and relieves the silencing of CS1 expression.