Regulation of Expression of the Region 3 Promoter of the Escherichia coli K5 Capsule Gene Cluster Involves H-NS, SlyA, and a Large 5′ Untranslated Region

ABSTRACT Escherichia coli group 2 capsule gene clusters are temperature regulated, being expressed at 37°C but not at 20°C. Expression is regulated at the level of transcription by two convergent promoters, PR1 and PR3. In this paper, we show that regulation of transcription from PR3 involves a number of novel features including H-NS, SlyA, and a large 741-bp 5′ untranslated region (UTR). H-NS represses transcription from PR3 at 20°C and binds both 5′ and 3′ of the transcription start site. The 3′ downstream regulatory element (DRE) was essential for temperature-dependent H-NS repression. At 37°C, SlyA activates transcription independent of H-NS but maximal transcription requires H-NS. The UTR is present between the transcription start site and the first gene in the operon, kpsM . We demonstrate that the UTR, as well as containing the H-NS DRE, functions to moderate the extent of transcription that reaches kpsM and allows the binding of antitermination factor RfaH.