Clark A B, Valle F, Drotschmann K, Gary R K, Kunkel T A
Laboratory of Molecular Genetics and Laboratory of Structural Biology, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
J Biol Chem. 2000 Nov 24;275(47):36498-501. doi: 10.1074/jbc.C000513200.
Eukaryotic DNA mismatch repair requires the concerted action of several proteins, including proliferating cell nuclear antigen (PCNA) and heterodimers of MSH2 complexed with either MSH3 or MSH6. Here we report that MSH3 and MSH6, but not MSH2, contain N-terminal sequence motifs characteristic of proteins that bind to PCNA. MSH3 and MSH6 peptides containing these motifs bound PCNA, as did the intact Msh2-Msh6 complex. This binding was strongly reduced when alanine was substituted for conserved residues in the motif. Yeast strains containing alanine substitutions in the PCNA binding motif of Msh6 or Msh3 had elevated mutation rates, indicating that these interactions are important for genome stability. When human MSH3 or MSH6 peptides containing the PCNA binding motif were added to a human cell extract, mismatch repair activity was inhibited at a step preceding DNA resynthesis. Thus, MSH3 and MSH6 interactions with PCNA may facilitate early steps in DNA mismatch repair and may also be important for other roles of these eukaryotic MutS homologs.
真核生物的DNA错配修复需要几种蛋白质协同作用，包括增殖细胞核抗原（PCNA）以及与MSH3或MSH6复合的MSH2异二聚体。我们在此报告，MSH3和MSH6（而非MSH2）含有与PCNA结合的蛋白质所特有的N端序列基序。含有这些基序的MSH3和MSH6肽能与PCNA结合，完整的Msh2-Msh6复合物也能结合。当丙氨酸取代基序中的保守残基时，这种结合会大大减少。在Msh6或Msh3的PCNA结合基序中含有丙氨酸取代的酵母菌株具有较高的突变率，这表明这些相互作用对基因组稳定性很重要。当将含有PCNA结合基序的人MSH3或MSH6肽添加到人细胞提取物中时，错配修复活性在DNA重新合成之前的步骤受到抑制。因此，MSH3和MSH6与PCNA的相互作用可能有助于DNA错配修复的早期步骤，并且对于这些真核MutS同源物的其他作用也可能很重要。
