Regulatory mutations of lacI and lacO

(a) WildtypelacI and lacO. (b) Operator-constitutive (lacOC) mutation.(c) lacI- (operator-binding domain) mutation. (d) lacIS (superrepressor) mutation of the allosteric binding domain(a) WildtypelacI and lacO. (b) Operator-constitutive (lacOC) mutation.(c) lacI- (operator-binding domain) mutation. (d) lacIS (superrepressor) mutation of the allosteric binding domain

(a) It (wild type) Repressor binds operator when the inducer is absent and forms an inducer— repressor complex when inducer is present. Lac repressor protein Allolactose (b) O‘ (operator constitutive mutation) Operator-site mutation prevents repressor protein binding and leads to constitutive synthesis of the lac operon. Lac repressor protein (c) I‘(repressor mutation) Repressor protein mutation prevents repressor binding to the operator and produces constitutive M synthesis of the lac operon. uta nt protein (d) IS (super-repressor mutation) Repressor protein mutation blocks binding to the inducer, preventing formation of the inducer—repressor complex. Mutant repressor protein Super-repressor binds to the operator, mutant preventing transcription.