1887

Abstract

Heat-labile enterotoxin, a major virulence determinant of enterotoxigenic , is encoded by the operon. To elucidate the molecular mechanism by which the heat-stable nucleoid-structural (H-NS) protein controls transcription of , the authors constructed an transcriptional fusion and performed -galactosidase analysis. The results showed that H-NS protein exerts fivefold repression on transcription from the promoter at 37 °C and 10-fold repression at 22 °C. Two silencer regions that were required for H-NS-mediated repression of expression were identified, both of which were located downstream of the start site of transcription. One silencer was located between +31 and +110, the other between +460 and +556, relative to the start site of transcription, and they worked cooperatively in repression. DNA sequences containing the silencers were predicted to be curved by analysis and bound H-NS protein directly . Repression of transcription by H-NS was independent of promoter strength, and the presence of H-NS protein did not affect promoter opening , indicating that repression was achieved by inhibiting promoter clearance or blocking transcription elongation, probably via DNA looping between the two silencers.

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2005-04-01
2019-11-13
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