Inducer and anti-inducer interactions with the lac repressor seen by nuclear magnetic resonance changes at tyrosines and tryptophans.

The effects of binding inducer and anti-inducer of the Escherichia coli lac operon to the lac repressor were examined by taking advantage of fluorine-19 NMR. The fluorine nucleus was biosynthetically incorporated into the lac repressor with either 5-fluorotryptophan or 3-fluorotyrosine. It is suggested that these small effector molecules influence the operator-binding properties of the tetrameric lac repressor by altering the intersubunit relationships in the protein.