title: lac repressor changes conformation upon binding to poly[dA-T)].
abstract: N-(Iodoacetylaminoethyl)-1-naphthylamine-5-sulfonate reacts with Escherichia coli lac repressor to selectively label cysteine-140 with the fluorescent N-(acetylaminoethyl)-1-naphthylamine-5-sulfonate group. The fluorescence intensity of this label decreases by 20% when labeled repressor associates with poly[d(A-T)]. Fifteen base pairs of poly[d(A-T)] per repressor tetramer are required to complete this decrease. Stopped-flow experiments have shown that the repressor undergoes at least two conformational changes as it binds to poly[d(A-T)], with half-lives of 5.0 +/- 1.2 msec and 3.5 +/- 1.0 sex. Quite likely, these conformational changes serve to strengthen the interaction of repressor with DNA.
mesh_terms: D003545:Cysteine; D004926:Escherichia coli; D005456:Fluorescent Dyes; D007460:Iodoacetamide / Q000031:analogs & derivatives; D007700:Kinetics; D009282:Naphthalenesulfonates; D010446:Peptide Fragments / Q000032:analysis; D011067:Poly dA-dT; D011089:Polydeoxyribonucleotides; D011487:Protein Conformation; D012097:Repressor Proteins; D013050:Spectrometry, Fluorescence; D014157:Transcription Factors
chemical_list: D005456:Fluorescent Dyes; D009282:Naphthalenesulfonates; D010446:Peptide Fragments; D011089:Polydeoxyribonucleotides; D012097:Repressor Proteins; D014157:Transcription Factors; D011067:Poly dA-dT; D003545:Cysteine; D007460:Iodoacetamide