An Amino-Terminal Fragment of lac Repressor Binds Specifically to lac Operator

We have examined the effect of an aminoterminal peptide from the lac repressor (residues 1-59) on the methylation of purines in the lac operator with dimethyl sulfate. The peptide perturbs the methylation of the operator, and the peptide-induced pattern of inhibition and enhancement of methylation, across the operator, closely resembles the pattern induced by intact repressor. This demonstrates that this small amino-terminal peptide binds specifically to the lac operator and that the mechanism of recognition and binding is basically the same as that of intact repressor.