A comparison of lac repressor binding to operator and to nonoperator DNA

We have compared the operator and nonoperator DNA binding activities of the lac repressor with respect to inactivation or inhibition by trypsin, heat, actinomycin, and isopropylthiogal-actoside. The two DNA binding activities were found to differ only in their sensitivity to the inducing ligand isopropylthiogal-actoside. Repressor binding to poly(dT-dT-dG)·poly(dC-dA-dA) was shown not to be affected by isopropylthiogalactoside.