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lac repressor-operator interaction

1972; Elsevier BV; Volume: 64; Issue: 1 Linguagem: Inglês

10.1016/0022-2836(72)90328-2

1089-8638

Alan H. Jobe, Arthur D. Riggs, Suzanne Bourgeois,

Enzyme Structure and Function

Procedures are outlined for measuring inducer and operator binding of lac repressor in crude extract. For most experiments, including those measuring repressor-operator association rates, purification beyond ammonium sulfate fractionation is not required. Kinetic measurements have been used to differentiate repressors of three normally inducible strains. Repressor from strain C6000 binds operator more tightly than does repressor from E203, previously considered to be wild type and subjected to extensive analysis in this laboratory. Repressor from an overproducing (iq) strain is also different from either C6000 or E203. The repressor from extracts of two new is mutants, or super-repressors, are characterized by inducer and operator binding and are compared to previously characterized is mutants. All 11 super-repressors examined so far show a decreased affinity for inducer. Three have an increased affinity for operator and the other eight have normal operator binding. Three of the mutants are allosteric mutants in that the inducer response curves have a shape different from wild type.