Wharton R P, Ptashne M
Nature. 1987;326(6116):888-91. doi: 10.1038/326888a0.
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.
噬菌体434编码的阻遏蛋白通过将一个“识别”α-螺旋插入DNA的大沟来结合其操纵基因。我们确定了一个氨基酸-碱基对接触，它（部分）决定了434阻遏蛋白的DNA结合特异性。这一确定基于一个“新特异性”突变体Repressor [Ala 28]的特性，该突变体在其识别α-螺旋的第一个残基处发生了谷氨酰胺被丙氨酸取代的情况。Repressor [Ala 28]与一个特定的双重突变操纵基因具有高亲和力，该操纵基因在每个半位点的第1位都有相同的取代，但不与野生型操纵基因或其他突变操纵基因结合。我们描述了第28位残基与第1碱基对相互作用的分子模型，该模型解释了突变型和野生型蛋白的结合特异性。
