RESUMEN
The crystal structure of the amino-terminal domain of phage 434 repressor has been solved using molecular replacement methods and refined to an R-factor of 19.3% against data to 2.0 A resolution. The protein comprises five short alpha-helices. Two of these form a helix-turn-helix motif, very similar to those found in related proteins. The protein is remarkably similar to the Cro protein from the same phage.
Asunto(s)
Bacteriófagos/genética , Proteínas Represoras/genética , Factores de Transcripción/genética , Proteínas Virales/genética , Secuencia de Aminoácidos , Proteínas de Unión al ADN/genética , Modelos Moleculares , Datos de Secuencia Molecular , Conformación Proteica , Proteínas Reguladoras y Accesorias Virales , Difracción de Rayos XRESUMEN
The repressors of temperate bacteriophages such as 434 and lambda control transcription by binding to a set of DNA operator sites. The different affinity of repressor for each of these sites ensures efficient regulation. High-resolution x-ray crystallography was used to study the DNA-binding domain of phage 434 repressor in complex with a synthetic DNA operator. The structure shows recognition of the operator by direct interactions with base pairs in the major groove, combined with the sequence-dependent ability of DNA to adopt the required conformation on binding repressor. In particular, a network of three-centered bifurcated hydrogen bonds among base pairs in the operator helps explain why 434 repressor prefers certain sites over others. These bonds, which stabilize the conformation of the bound DNA, can form only with certain sequences.