A sister-strand exchange mechanism for recA-independent deletion of repeated DNA sequences in Escherichia coli.
A sister-strand exchange mechanism for recA-independent deletion of repeated DNA sequences in Escherichia coli.
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发表时间：
1993-11
期刊：
影响因子：
3.3
通讯作者：
S. Lovett;P. T. Drapkin;V. Sutera;T. J. Gluckman-Peskind
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作者：
S. Lovett;P. T. Drapkin;V. Sutera;T. J. Gluckman-Peskind
在许多生物体的基因组中，串联重复的DNA序列之间出现缺失，长度从几千个碱基到只有几个核苷酸不等。使用基于质粒的测定787-bp串联重复序列的缺失，我们发现一个不依赖reca的机制在很大程度上促进了这个大区域同源性的缺失过程。测试的大肠杆菌重组基因，包括recA，对缺失率的影响都没有超过5倍。缺失形成的reca独立性也被观察到存在于染色体上的结构。RecA在体外促进同源DNA链的突触和转移，并且在偶联后测量的体内分子间重组事件中是必不可少的。由于大肠杆菌中缺失的形成对recA的依赖性很小或没有依赖性，因此人们一直认为同源重组对缺失过程的贡献很小。然而，我们发现，当ruvA突变抑制细胞中的分支迁移时，reca不依赖的缺失产物提示了相互交叉。我们提出了一个复制姐妹链之间reca独立交叉的模型，这也可以解释重复序列的缺失或扩增。我们认为这一过程可能始于复制后DNA修复；随后在重复序列上的链错位导致基因重排。
In the genomes of many organisms, deletions arise between tandemly repeated DNA sequences of lengths ranging from several kilobases to only a few nucleotides. Using a plasmid-based assay for deletion of a 787-bp tandem repeat, we have found that a recA-independent mechanism contributes substantially to the deletion process of even this large region of homology. No Escherichia coli recombination gene tested, including recA, had greater than a fivefold effect on deletion rates. The recA-independence of deletion formation is also observed with constructions present on the chromosome. RecA promotes synapsis and transfer of homologous DNA strands in vitro and is indispensable for intermolecular recombination events in vivo measured after conjugation. Because deletion formation in E. coli shows little or no dependence on recA, it has been assumed that homologous recombination contributes little to the deletion process. However, we have found recA-independent deletion products suggestive of reciprocal crossovers when branch migration in the cell is inhibited by a ruvA mutation. We propose a model for recA-independent crossovers between replicating sister strands, which can also explain deletion or amplification of repeated sequences. We suggest that this process may be initiated as post-replicational DNA repair; subsequent strand misalignment at repeated sequences leads to genetic rearrangements.