Specificity determinants for the interaction of λ repressor and P22 repressor dimers

• Published in: Genes & development 1994-05, Vol.8 (10), p.1212-1223
• Main Authors: WHIPPLE, F. W, KULDELL, N. H, CHEATHAM, L. A, HOCHSCHILD, A
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Base Sequence; Biological and medical sciences; Conserved Sequence; DNA, Viral - metabolism; DNA-Binding Proteins; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Viral - physiology; Genetics; Microbiology; Models, Genetic; Molecular Sequence Data; Operator Regions, Genetic - genetics; Operator Regions, Genetic - physiology; phage lambda; phage P22; Point Mutation - physiology; Protein Conformation; Recombinant Fusion Proteins - metabolism; Repressor Proteins - chemistry; Repressor Proteins - metabolism; Transcription, Genetic - physiology; Viral Proteins; Viral Regulatory and Accessory Proteins; Virology
• ISSN: 0890-9369; 1549-5477
• DOI: 10.1101/gad.8.10.1212

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.