title: lac repressor-lac operator interaction: NMR observations.
abstract: We show here the changes in the NMR spectra of the Escherichia coli lac repressor when bound to isolated lac operator DNA. The observations focus on the aromatic residues--four tyrosines and a single histidine--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 1 H NMR of otherwise identical repressor--DNA complexes. The results suggest that the tyrosines 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 two amino-terminal fragments per operator in the specific complex.
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D004269:DNA, Bacterial / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D005786:Gene Expression Regulation; D007763:Lac Operon; D009682:Magnetic Resonance Spectroscopy; D010446:Peptide Fragments; D011485:Protein Binding; D012097:Repressor Proteins / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000378:metabolism*; D014443:Tyrosine
chemical_list: D004269:DNA, Bacterial; D010446:Peptide Fragments; D012097:Repressor Proteins; D014157:Transcription Factors; D014443:Tyrosine