Schaaper R M, Dunn R L
Proc Natl Acad Sci U S A. 1987 Sep;84(17):6220-4. doi: 10.1073/pnas.84.17.6220.
We have determined the DNA sequence changes in 487 spontaneous mutations in the N-terminal part of the lacI gene in mutH, mutL, and mutS strains of Escherichia coli. These strains display elevated spontaneous mutation rates because of a deficiency in the process of postreplicative mismatch correction. As a consequence the mutational spectra reveal the nature of spontaneous DNA replication errors. The spectra consist of base substitutions (75%) and single-base deletions (25%). Among the base substitutions, transitions (both A.T----G.C and G.C----A.T) are strongly favored over transversions (96% versus 4%). Large site-to-site differences are observed among identical base substitutions, presumably reflecting the modulating effects of neighboring bases. The single-base-deletion spectrum is dominated by a large hotspot at a run of adjacent identical base pairs, implying a Streisinger-slippage mechanism. The data, when compared to a previously determined wild-type spectrum, also provide information on the specificity of the mismatch repair system.
我们已经确定了大肠杆菌mutH、mutL和mutS菌株中lacI基因N端487个自发突变的DNA序列变化。由于复制后错配修复过程存在缺陷，这些菌株表现出自发突变率升高。因此，突变谱揭示了自发DNA复制错误的本质。该谱由碱基替换（75%）和单碱基缺失（25%）组成。在碱基替换中，转换（A.T→G.C和G.C→A.T）比颠换更受青睐（96%对4%）。在相同的碱基替换中观察到较大的位点间差异，这可能反映了相邻碱基的调节作用。单碱基缺失谱主要由一段相邻相同碱基对处的一个大热点主导，这意味着存在斯特赖辛格滑动机制。与先前确定的野生型谱相比，这些数据还提供了错配修复系统特异性的信息。
