title: Specificity determinants for the interaction of lambda repressor and P22 repressor dimers.
abstract: The related phage lambda and phage P22 repressors each bind cooperatively to adjacent and separated operator sites, an interaction that involves a pair of repressor dimers. The specificities of these interactions differ: Each dimer interacts with its own type but not with dimers of the heterologous repressor. The two repressors exhibit significant amino acid sequence homology in their carboxy-terminal domains, which are responsible for both dimer formation and the dimer-dimer interaction. Here, we identify a collection of amino acid substitutions that disrupt the protein-protein interaction of DNA-bound lambda repressor dimers and show that several of these substitutions have the same effect when introduced at the corresponding positions of P22 repressor. We use this information to construct a variant of the lambda repressor bearing only six non-wild-type amino acids that has a switched specificity; that is, it binds cooperatively with P22 repressor, but not with wild-type lambda repressor. These results identify a series of residues that determine the specificities of the two interactions.
authors.affiliation: Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: F W
authors.initials: FW
authors.lastname: Whipple
authors.forename: N H
authors.initials: NH
authors.lastname: Kuldell
authors.forename: L A
authors.initials: LA
authors.lastname: Cheatham
authors.forename: A
authors.initials: A
authors.lastname: Hochschild
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D017124:Conserved Sequence; D004279:DNA, Viral / Q000378:metabolism*; D004268:DNA-Binding Proteins; D015967:Gene Expression Regulation, Viral / Q000502:physiology; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009875:Operator Regions, Genetic / Q000235:genetics / Q000502:physiology; D017354:Point Mutation / Q000502:physiology; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology*; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins
chemical_list: D004279:DNA, Viral; D004268:DNA-Binding Proteins; C034261:P22 repressor protein, Enterobacteria phage P22; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins; C016649:phage repressor proteins