The nucleoid-associated DNA-binding protein H-NS is required for the efficient adaptation of Escherichia coli K-12 to a cold environment

Abstract

The hns gene is a member of the cold-shock regulon, indicating that the nucleoid-associated, DNA-binding protein H-NS plays an important role in the adaptation of Escherichia coli to low temperatures. We show here that the ability to cope efficiently with a cold environment (12 degrees C and 25 degrees C) is strongly impaired in E. coli strains carrying hns mutations. Growth inhibition is much more pronounced in strains carrying the hns-206 allele (an ampicillin resistance cassette inserted after codon 37) than in those carrying the hns-205 mutation (a Tn10 insertion located in codon 93). A protein fragment (H-NS*) is synthesized in strains carrying the hns-205::Tn10 mutation, suggesting that this truncated polypeptide is partially functional in the cold adaptation process. Analysis of the growth properties of strains harbouring four different low-copy-number plasmid-encoded hns' genes that result in the production of C-terminally truncated H-NS proteins supports this proposal. H-NS* proteins composed of 133, 117 or 94 amino-terminal amino acids partially complemented the severe cold-sensitive growth phenotype of the hns-206 mutant. In contrast, synthesis of a truncated H-NS protein with only 75 amino-terminal amino acids was insufficient to restore growth at low temperature.