Characterization of i−d repressor mutations of the lactose operon

Abstract

A set of dominant mutations in the lacI gene (iq–d mutants) has been obtained and characterized as to repression of the lactose operon in vivo. Studies of inducer and operator binding in vitro have been done on repressors from representative mutants. Several types of mutations are experimentally distinguished, including one which affects both operator and inducer affinities of the repressor. Another type appears to affect the stability of the repressor in vivo. Operator binding studies in vitro demonstrate the presence of mixed (iq+/iq–d) repressor tetramers in extracts of cells carrying both alleles of the i gene.