Effect of mutations in dnaK and dnaJ genes on cysteine operon expression in Escherichia coli.

The effect of mutations in dnaK and dnaJ genes on the expression of two operons that are part of cysteine regulon was determined using Escherichia coli strains harboring cysPTWA::lacZ and cysJIH::lacZ fusions. Null dnaJ and dnaKdnaJ mutants were impaired in beta-galactosidase expression from both fusions. Efficient complementation of this defect by wild-type alleles present on a low-copy number plasmid was achieved. The presence of the pMH224 plasmid coding for CysB* protein defective in DNA binding lowered beta-galactosidase expression from cysPTWA::lacZ fusion strain harboring wild-type dnaKdnaJ alleles but did not diminish enzyme expression in delta dnaJ and delta dnaKdnaJ strains.