Portal de Periódicos da CAPES

lac repressor—Operator interaction

1970; Elsevier BV; Volume: 51; Issue: 2 Linguagem: Inglês

10.1016/0022-2836(70)90144-0

1089-8638

Arthur D. Riggs, Ronald F. Newby, Suzanne Bourgeois,

Ion Transport and Channel Regulation

A membrane filter technique was used to study the effect of galactosides and other low molecular weight compounds on the interaction of purified lac repressor and lac operator. Compounds that function in vivo as inducers of the lac operon are found to inhibit repressor-operator binding in vitro. Compounds that prevent induction in vivo are found to counteract the effect of inducers in vitro. The order of effectiveness of these compounds is the same in vitro as in vivo and agrees with their affinity for the lac repressor. Glucose interacts with the lac repressor and behaves as a weak anti-inducer. Cyclic adenosine monophosphate was found to have no effect on repressor-operator binding. The effect of galactosides on the rate of dissociation of repressor-operator complexes was also studied. The rate of dissociation was found to be increased by an inducer, isopropyl-β-d-thiogalactoside, and decreased by an anti-inducer, o-nitrophenyl-β-d-fucoside. This result has implications both in regard to allosteric models for conformational changes in proteins and in regard to the interpretation of both in vivo and in vitro induction curves.