title: Binding of lactose repressor to poly d(A-T) : OD AND CD melting of the complex.
abstract: The binding of lactose repressor to poly d(A-T) at low ionic strength has been investigated by heat denaturation. The poly d(A-T) melting is monitored by optical density and the protein melting by circular dichroism. From the modification of the poly d(A-T) melting curve we estimate a maximum binding ratio of about one tetrameric repressor to about 20 basic pairs. The repressor melting can be interpreted as a global shift from a to b structure of about 25 residues per subunit. The melting curves of poly d(A-T) and repressor have not a shape easy to interpret; nevertheless both show a cooperative transition in the same temperature range where we can evaluate that about 3.8 aminoacid residues shift from a to b structure when 1 bases pair melt.
mesh_terms: D000227:Adenine Nucleotides; D001426:Bacterial Proteins; D001665:Binding Sites; D002942:Circular Dichroism; D004269:DNA, Bacterial; D003854:Deoxyribonucleotides; D004926:Escherichia coli / Q000378:metabolism; D006358:Hot Temperature; D007700:Kinetics; D007785:Lactose / Q000378:metabolism; D009154:Mutation; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D011119:Polynucleotides; D011485:Protein Binding; D011487:Protein Conformation; D013056:Spectrophotometry, Ultraviolet; D013942:Thymine Nucleotides
chemical_list: D000227:Adenine Nucleotides; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D003854:Deoxyribonucleotides; D011119:Polynucleotides; D013942:Thymine Nucleotides; D007785:Lactose