Proton NMR study of a complex between the lac repressor headpiece and a 22 base pair symmetric lac operator

Abstract

A complex between the lac repressor headpiece and a fully symmetric tight-binding 22 bp lac operator was studied by 2D NMR. Several 2D NOE spectra were recorded for the complex in both H2O and 2H2O. Many NOE cross-peaks between the headpiece and DNA could be identified, and changes in the chemical shift of the DNA protons upon complex formation were analyzed. Comparison of these data with those obtained for a complex between the headpiece and a 14 bp half-operator, studied previously [Boelens, R., Scheek, R. M., Lamerichs, R. M. J. N., de Vlieg. J., van Boom, J. H., and Kaptein, R. (1987) in DNA-ligand interactions (Guschlbauer, W., and Saenger, W., Eds.)pp 191-215, Plenum, New York], shows that two headpieices form a specific complex with a 22 bp lac operator in which each headpiece binds in the same way as found for the 14 bp complex. The orientation of the recognition helix in the major groove in DNA in these complexes is opposite with respect to the dyad axis to that found for other repressors.