Autoregulatory expression of the Escherichia coli hns gene encoding a nucleoid protein: H-NS functions as a repressor of its own transcription.

The Escherichia coli nucleoid protein, H-NS (or H1a), appears to influence the regulation of a variety of unrelated E. coli genes and operons. To gain an insight into the regulation of the hns gene itself, we constructed in this study a hns-lacZ transcriptional fusion gene and inserted a single copy at the att lambda locus on the E. coli chromosome. Expression of hns transcription appeared to be moderately regulated in a growth phase-dependent manner. It also emerged that hns transcription is under negative autoregulation, at least in the logarithmic growth phase. The results of in vitro transcription experiments confirmed that H-NS functions as a repressor for its own transcription. Thus, H-NS was shown to exhibit relatively high affinity for the DNA sequence encompassing the hns promoter region, as compared with a non-specific sequence. These results support the view that the nucleoid protein, H-NS, can function as a transcriptional regulator.