[Effect of an inducer on orientation of the DNA-binding domain of the Lac repressor].

We have identified the lac repressor amino acids which form cross-links with partially depurinated DNA and hence are proximate to it. Only lysine-33 is cross-linkable in specific complex with lac operator. At the presence of inducer molecules lysine-33 remains cross-linkable. However, the N-terminal alpha-aminogroup was additionally cross-linked with the boundaries of lac operator. We conclude that orientation of the DNA-binding domain of the repressor is reversed by inducer binding.