lac repressor-lac operator interaction: NMR observations.

Abstract

Changes that occur in the NMR spectra of the Escherichia coli lac repressor when bound to isolated lac operator DNA were studied. The observations focus on the aromatic residues 4 tyrosines and a single histidine.sbd.in the amino-terminal DNA binding domain of the lac repressor. There is a good correlation between chemical shift changes seen by 19F NMR when compared with 1H NMR of otherwise identical repressor-DNA complexes. The tyrosines apparently do not intercalate in the DNA. The NMR spectral changes with similarly sized DNA fragments, not containing the lac operator DNA sequence, are different. Thus, the amino-terminal domain of the lac repressor is independently capable of discriminating between lac operator and nonspecific DNA sequences. There can be 2 amino-terminal fragments per operator in the specific complex.