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Interactions of the nucleoid-associated DNA-binding protein H-NS with the regulatory region of the osmotically controlled proU operon of Escherichia coli
Ist Teil von
The Journal of biological chemistry, 1994-03, Vol.269 (9), p.6578-6586
Ort / Verlag
Bethesda, MD: American Society for Biochemistry and Molecular Biology
The Escherichia coli hns gene encodes the abundant nucleoid-associated DNA-binding protein H-NS. Mutations in hns alter the
expression of many genes with unrelated functions and result in a derepression of the proU operon (proVWX) without abolishing
the osmotic control of its transcription. We have investigated the interactions of H-NS with the proU regulatory region by
deletion analysis of cis-acting sequences, competitive gel retardation assays, and DNase I footprinting. The negative effect
of H-NS on proU transcription was mediated by cis-acting sequences within proV but did not depend on the presence of a curved
DNA segment upstream of the proU-35 region previously characterized as a target for H-NS binding in vitro. We detected a 46-base
pair high affinity H-NS binding region downstream of the proU promoter at the 5' end of the proV gene and a complex array
of additional H-NS binding sites which suggest the presence of an extended H-NS nucleoprotein complex. Most of the H-NS binding
sites were highly A+T-rich and carried stretches of 5 or more consecutive A-T base pairs. The implications of our results
for the osmotic regulation of proU transcription are discussed.