Complex of lac repressor headpiece with a 14 base-pair lac operator fragment studied by two-dimensional nuclear magnetic resonance.

Two-dimensional nuclear Overhauser enhancement spectra are presented of the complex of lac repressor headpiece with a 14 base-pair lac operator fragment. Analysis of nuclear Overhauser enhancements observed between protein and DNA shows that the second helix of the headpiece ("the recognition helix") binds in the major groove of DNA as has been suggested, but that the orientation of this helix is approximately 180 degrees different from the proposed models.