title: A new-specificity mutant of 434 repressor that defines an amino acid-base pair contact.
abstract: The repressor encoded by bacteriophage 434 binds to its operators by inserting a 'recognition' alpha-helix into the major groove of the DNA. We have identified an amino acid-base pair contact that determines (in part) the DNA-binding specificity of 434 repressor. The identification is based on the properties of a 'new-specificity' mutant, named Repressor [Ala 28], which bears the substitution of Ala for Gln at the first residue of its recognition alpha-helix. Repressor [Ala 28] binds with high affinity to a particular doubly mutant operator bearing the same substitution at position 1 in each half-site, but does not bind to either the wild-type operator or to other mutant operators. We describe molecular models of residue 28-base pair 1 interactions that account for the binding specificities of both the mutant and wild-type proteins.
mesh_terms: D044503:5-Methylcytosine; D001482:Base Composition; D003090:Coliphages / Q000235:genetics* / Q000378:metabolism; D003596:Cytosine / Q000031:analogs & derivatives / Q000378:metabolism; D004269:DNA, Bacterial / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D009690:Nucleic Acid Conformation; D009875:Operator Regions, Genetic; D011485:Protein Binding; D011487:Protein Conformation; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics*; D014764:Viral Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D004269:DNA, Bacterial; D012097:Repressor Proteins; D014157:Transcription Factors; D014764:Viral Proteins; D044503:5-Methylcytosine; D003596:Cytosine