Leach D R, Okely E A, Pinder D J
Institute of Cell and Molecular Biology, University of Edinburgh, UK.
Mol Microbiol. 1997 Nov;26(3):597-606. doi: 10.1046/j.1365-2958.1997.6071957.x.
We report here that homologous recombination functions are required for the viability of Escherichia coli cells maintaining a 240 bp chromosomal inverted repeat (palindromic) sequence. Wild-type cells can successfully replicate this palindrome but recA, recB or recC mutants carrying the palindrome are unviable. The dependence on homologous recombination for cell viability is overcome in sbcC mutants. Directly repeated copies of the DNA containing the palindrome are rapidly resolved to single copies in wild-type cells but not in sbcC mutants. Our results suggest that double-strand breaks introduced at the palindromic DNA sequence by the SbcCD nuclease are repaired by homologous recombination. The repair is conservative and the palindrome is retained in the repaired chromosome. We conclude that SbcCD can attack secondary structures but that repair conserves the DNA sequence with the potential to fold.
我们在此报告,维持一段240 bp染色体反向重复(回文)序列的大肠杆菌细胞的生存能力需要同源重组功能。野生型细胞能够成功复制这段回文序列,但携带该回文序列的recA、recB或recC突变体无法存活。在sbcC突变体中,细胞生存能力对同源重组的依赖性得以克服。在野生型细胞中,含有回文序列的DNA的直接重复拷贝会迅速解析为单拷贝,而在sbcC突变体中则不会。我们的结果表明,由SbcCD核酸酶在回文DNA序列处引入的双链断裂通过同源重组进行修复。这种修复是保守的,回文序列保留在修复后的染色体中。我们得出结论,SbcCD可以攻击二级结构,但修复过程保留了具有折叠潜力的DNA序列。