Mutations in a gene encoding a new Hsp70 suppress rapid DNA inversion and bgl activation, but not proU derepression, in hns-1 mutant Escherichia coli.

Mutations in hns, the gene encoding the nucleoid-associated protein H-NS, affect both the expression of many specific unlinked genes and the inversion rate of the DNA segment containing the pilA promoter in Escherichia coli. A second-site mutation, termed hscA1, compensated for the effect of an hns-1 mutant allele on the pilA promoter inversion rate and on activation of the bgl operon. The proU operon, induced in an hns-1 background, remained derepressed in an hns-1 hscA1 strain and was induced at an intermediate level in an hns hscA1 strain. An insertion mutant allele, hscA2-cat, conferred the same partial hns-1 compensatory phenotype as the hscA1 allele. The hscA gene encoded a 66-kDa protein product that is a member of the Hsp70 protein class. The gene encoding this product is part of a bicistronic operon that is preceded by a possible sigma 32 promoter and also encodes a 21-kDa protein with significant homology to the DnaJ protein family. The mutation defining the hscA1 allele resulted in a phenylalanine substituting a conserved serine residue located in the ATP-binding region of other Hsp70 proteins.