title: Association of Escherichia coli lac repressor with poly[d(A-T)] monitored with 8-anilino-1-napthalenesulfonate.
abstract: The association of lac repressor with poly[d(A-T)] was monitored with the fluorescent prob 8-anilino-1-naphthalenesulfonate (Ans). Excess poly[d(A-T)] decreased the emission intensity of the repressor--Ans complex by 30%. Fluorescence titrations indicated that 33 +/- 4 base pairs were required to bind all of the repressor. Sedimentation studies indicated, however, that all of the repressor sedimented as a protein--DNA complex with as few as 10 to 15 base pairs per tetramer, even in the presence of Ans. These data are interpreted with two models: one where repressors bind to both sides of the DNA (Butler, A. P., et al. (1977) Biochemistry 16, 4757: Zingsheim, H.P., et al. (1977) J. Mol. Biol. 115, 565), the other where a double layer of repressors bind to a single side of the DNA. Removal of the amino-terminal regions from the repressor decreased the fluorescence from bound Ans by 77%. The amino-terminal fragments alone did not enhance Ans fluorescence.
mesh_terms: D000817:Anilino Naphthalenesulfonates; D003460:Crystallization; D004926:Escherichia coli / Q000378:metabolism*; D007700:Kinetics; D011067:Poly dA-dT; D011089:Polydeoxyribonucleotides; D011485:Protein Binding; D012097:Repressor Proteins / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D000817:Anilino Naphthalenesulfonates; D011089:Polydeoxyribonucleotides; D012097:Repressor Proteins; D014157:Transcription Factors; D011067:Poly dA-dT