[Isolation of mutants with impaired retroinhibition of histidine biosynthesis]

The Escherichia coli, strain possessing purF, deoD and add mutations converts exogenous adenine into guanine nucleotides exclusively by the pathway coupled with histidine biosynthesis. When grown on adenine, this strain demonstrated sensitivity to histidine, thus making it possible to select histidine-resistant hisGR mutants with ATP-phosphoribosyltransferase desensibilized for histidine. The hisGR mutations were obtained in two his operons introduced into the his operon-sensitive E. coli strain: his operon of Salmonella typhimurium incorporated in DNA and his operon of E. coli on the F'episome. In both cases, the hisGR mutants obtained were shown to excrete histidine.