title: In vitro interaction of the Escherichia coli cyclic AMP receptor protein with the lactose repressor.
abstract: Sedimentation equilibrium studies show that the Escherichia coli cyclic AMP receptor protein (CAP) and lactose repressor associate to form a 2:1 complex in vitro. This is, to our knowledge, the first demonstration of a direct interaction of these proteins in the absence of DNA. No 1:1 complex was detected over a wide range of CAP concentrations, suggesting that binding is highly cooperative. Complex formation is stimulated by cAMP, with a net uptake of 1 equivalent of cAMP per molecule of CAP bound. Substitution of the dimeric lacI-18 mutant repressor for tetrameric wild-type repressor completely eliminates detectable binding. We therefore propose that CAP binds the cleft between dimeric units in the repressor tetramer. CAP-lac repressor interactions may play important roles in regulatory events that take place at overlapping CAP and repressor binding sites in the lactose promoter.
authors.affiliation: Department of Biochemistry and Molecular Biology, Penn State University College of Medicine, Hershey, Pennsylvania 17033, USA. mfried@psu.edu
authors.forename: M G
authors.initials: MG
authors.lastname: Fried
authors.forename: M A
authors.initials: MA
authors.lastname: Daugherty
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D002373:Cyclic AMP Receptor Protein / Q000737:chemistry / Q000378:metabolism*; D004926:Escherichia coli / Q000737:chemistry / Q000378:metabolism*; D029968:Escherichia coli Proteins; D056968:Lac Repressors; D011485:Protein Binding; D012097:Repressor Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D002373:Cyclic AMP Receptor Protein; D029968:Escherichia coli Proteins; D056968:Lac Repressors; C539064:LacI protein, E coli; D012097:Repressor Proteins