An rpoH gene that encodes a .sigma..sup.32 protein in which cysteine instead of arginine is at amino acid residue 268 was isolated from a mutant of Escherichia coli strain W3110. The rpoH gene has thymine instead of cytosine at the nucleotide position corresponding to 802 in the wild-type rpoH gene. Purified strains of E. coli W3110 and JM101 having a mutant rpoH gene in which thymine instead of cytosine is at the nucleotide position corresponding to 802 in a wild-type rpoH gene and a method for synthesis of proteins at enhanced levels are also disclosed. The method comprises introducing an expression vehicle into an E. coli strain containing the mutant rpoH gene of this invention.
