1887

Abstract

Silencing of the operon by the histone-like nucleoid-structuring protein H-NS occurs at two levels. Binding of H-NS upstream of the promoter represses transcription initiation, whilst binding within the coding region is also proposed to repress transcription elongation. The latter, downstream level of repression is counteracted by the protease Lon and, thus, silencing of the operon is more effective in mutants. Transposon-mutagenesis screens for suppression of this phenotype on were performed and insertion mutations disrupting and were obtained, as well as mutations mapping upstream of the open reading frames of , and . In and mutants, promoter activity is known to be higher. Likewise, as shown here, promoter activity is increased in the and mutants, which express BglJ and LeuO constitutively. However, BglJ and LeuO have no impact on downstream repression. A mutant was isolated for the first time in the context of the operon. The mutant expresses lower levels of DnaK than the wild-type. Interestingly, in this  : : miniTn mutant, downstream repression of by H-NS is less effective, whilst upstream repression by H-NS remains unaffected. Together, the data show that the two levels of silencing by H-NS are regulated independently.

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2005-10-01
2019-10-23
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