Brown T C, Jiricny J
Cell. 1987 Sep 11;50(6):945-50. doi: 10.1016/0092-8674(87)90521-6.
5-Methylcytosine spontaneously deaminates to form thymine, thus generating G/T mispairs in DNA. We investigated the way in which these lesions are addressed in mammalian cells by introducing specific G/T mispairs into the genome of SV40 and determining the fate of the mismatched bases in simian cells. Mispairs were incorporated in 12 bp synthetic duplexes ligated into SV40 DNA between the BstXI and TaqI restriction sites. Analysis of 347 plaques obtained after transfection of this modified DNA indicated that mispairs were corrected in 343 cases (99%), revealing 314 repair events in favor of guanine (90%) and 29 in favor of thymine (8%). Correction in favor of guanine occurred regardless of the orientation of the mispair in DNA and regardless of whether the mispair was in the commonly methylated CpG dinucleotide. These results attest to a specific mismatch repair pathway that restores G/C pairs lost through deamination of 5-methylcytosine residues.
5-甲基胞嘧啶会自发脱氨形成胸腺嘧啶，从而在DNA中产生G/T错配。我们通过将特定的G/T错配引入SV40基因组并确定猿猴细胞中错配碱基的命运，来研究哺乳动物细胞处理这些损伤的方式。错配被整合到12个碱基对的合成双链体中，该双链体连接到SV40 DNA的BstXI和TaqI限制位点之间。对转染这种修饰DNA后获得的347个噬菌斑进行分析表明，343例（99%）中的错配得到了校正，显示出314次偏向鸟嘌呤的修复事件（90%）和29次偏向胸腺嘧啶的修复事件（8%）。无论错配在DNA中的方向如何，也无论错配是否位于常见的甲基化CpG二核苷酸中，都发生了偏向鸟嘌呤的校正。这些结果证明了一种特定的错配修复途径，该途径可恢复因5-甲基胞嘧啶残基脱氨而丢失的G/C对。
