Lühr B, Scheller J, Meyer P, Kramer W
Institut für Molekulare Genetik, Georg-August-Universität Göttingen, Germany.
Mol Gen Genet. 1998 Feb;257(3):362-7. doi: 10.1007/s004380050658.
We have analysed the correction of defined mismatches in wild-type and msh2, msh3, msh6 and msh3 msh6 mutants of Saccharomyces cerevisiae in two different yeast strain backgrounds by transformation with plasmid heteroduplex DNA constructs. Ten different base/base mismatches, two single-nucleotide loops and a 38-nucleotide loop were tested. Repair of all types of mismatches was severely impaired in msh2 and msh3 msh6 mutants. In msh6 mutants, repair efficiency of most base/base mismatches was reduced to a similar extent as in msh3 msh6 double mutants. G/T and A/C mismatches, however, displayed residual repair in msh6 mutants in one strain background, implying a role for Msh3p in recognition of base/base mismatches. Furthermore, the efficiency of repair of base/base mismatches was considerably reduced in msh3 mutants in one strain background, indicating a requirement for MSH3 for fully efficient mismatch correction. Also the efficiency of repair of the 38-nucleotide loop was reduced in msh3 mutants, and to a lesser extent in msh6 mutants. The single-nucleotide loop with an unpaired A was less efficiently repaired in msh3 mutants and that with an unpaired T was less efficiently corrected in msh6 mutants, indicating non-redundant functions for the two proteins in the recognition of single-nucleotide loops.
我们通过用质粒异源双链DNA构建体转化，在两种不同的酵母菌株背景下，分析了酿酒酵母野生型以及msh2、msh3、msh6和msh3 msh6突变体中特定错配的校正情况。测试了十种不同的碱基/碱基错配、两个单核苷酸环和一个38核苷酸环。在msh2和msh3 msh6突变体中，所有类型错配的修复都严重受损。在msh6突变体中，大多数碱基/碱基错配的修复效率降低到与msh3 msh6双突变体相似的程度。然而，在一种菌株背景下，msh6突变体中G/T和A/C错配显示出残留修复，这意味着Msh3p在识别碱基/碱基错配中起作用。此外，在一种菌株背景下，msh3突变体中碱基/碱基错配的修复效率显著降低，表明完全有效的错配校正需要MSH3。msh3突变体中38核苷酸环的修复效率也降低，msh6突变体中的降低程度较小。带有未配对A的单核苷酸环比带有未配对T的单核苷酸环在msh3突变体中修复效率更低，表明这两种蛋白质在识别单核苷酸环中具有非冗余功能。
