RESUMEN
DNA mismatch repair ensures genomic integrity on DNA replication. Recognition of a DNA mismatch by a dimeric MutS protein initiates a cascade of reactions and results in repair of the newly synthesized strand; however, details of the molecular mechanism remain controversial. Here we present the crystal structure at 2.2 A of MutS from Escherichia coli bound to a G x T mismatch. The two MutS monomers have different conformations and form a heterodimer at the structural level. Only one monomer recognizes the mismatch specifically and has ADP bound. Mismatch recognition occurs by extensive minor groove interactions causing unusual base pairing and kinking of the DNA. Nonspecific major groove DNA-binding domains from both monomers embrace the DNA in a clamp-like structure. The interleaved nucleotide-binding sites are located far from the DNA. Mutations in human MutS alpha (MSH2/MSH6) that lead to hereditary predisposition for cancer, such as hereditary non-polyposis colorectal cancer, can be mapped to this crystal structure.
Asunto(s)
Proteínas Bacterianas/fisiología , Disparidad de Par Base , Reparación del ADN , ADN Bacteriano/química , Proteínas de Unión al ADN/química , Proteínas de Escherichia coli , Adenosina Trifosfatasas/metabolismo , Proteínas Bacterianas/genética , Sitios de Unión , Neoplasias Colorrectales Hereditarias sin Poliposis/genética , Cristalografía por Rayos X , ADN Bacteriano/metabolismo , Proteínas de Unión al ADN/metabolismo , Dimerización , Escherichia coli/química , Escherichia coli/metabolismo , Guanina/metabolismo , Humanos , Hidrólisis , Modelos Moleculares , Proteína MutS de Unión a los Apareamientos Incorrectos del ADN , Proteína 2 Homóloga a MutS , Mutación , Conformación de Ácido Nucleico , Conformación Proteica , Proteínas Proto-Oncogénicas/genética , Proteínas Proto-Oncogénicas/fisiología , Timina/metabolismoRESUMEN
Clones derived from SV40-transformed hamster lens cells have at least three different stable morphologies. Biochemical differences between the three cell types that become detectable after transfection of the alpha A-crystallin gene do exist at the level of alpha B-crystallin and small heat shock protein (HSP27) expression. Furthermore one cell type is capable of alternative splicing of the hamster alpha A-crystallin gene, whereas another one cannot express alpha AIns-crystallin.