Maisnier-Patin S, Nordström K, Dasgupta S
Department of Cell and Molecular Biology, Biomedical Centre, Uppsala University, S-751 24 Uppsala, Sweden.
J Bacteriol. 2001 Oct;183(20):6065-73. doi: 10.1128/JB.183.20.6065-6073.2001.
The recombinational rescue of chromosome replication was investigated in Escherichia coli strains with the unidirectional origin oriR1, from the plasmid R1, integrated within oriC in clockwise (intR1(CW)) or counterclockwise (intR1(CC)) orientations. Only the intR1(CC) strain, with replication forks arrested at the terminus, required RecA for survival. Unlike the strains with RecA-dependent replication known so far, the intR1(CC) strain did not require RecBCD, RecF, RecG, RecJ, RuvAB, or SOS activation for viability. The overall levels of degradation of replicating chromosomes caused by inactivation of RecA were similar in oriC and intR1(CC) strains. In the intR1(CC) strain, RecA was also needed to maintain the integrity of the chromosome when the unidirectional replication forks were blocked at the terminus. This was consistent with suppression of the RecA dependence of the intR1(CC) strain by inactivating Tus, the protein needed to block replication forks at Ter sites. Thus, RecA is essential during asymmetric chromosome replication for the stable maintenance of the forks arrested at the terminus and for their eventual passage across the termination barrier(s) independently of the SOS and some of the major recombination pathways.
在大肠杆菌菌株中研究了染色体复制的重组拯救，这些菌株带有来自质粒R1的单向复制起点oriR1，其以顺时针（intR1(CW)）或逆时针（intR1(CC)）方向整合在oriC内。只有intR1(CC)菌株，其复制叉在终点处停滞，需要RecA才能存活。与目前已知的依赖RecA进行复制的菌株不同，intR1(CC)菌株的存活不需要RecBCD、RecF、RecG、RecJ、RuvAB或SOS激活。RecA失活导致的复制染色体降解的总体水平在oriC和intR1(CC)菌株中相似。在intR1(CC)菌株中，当单向复制叉在终点处受阻时，也需要RecA来维持染色体的完整性。这与通过使Tus失活来抑制intR1(CC)菌株对RecA的依赖性是一致的，Tus是在Ter位点阻止复制叉的蛋白质。因此，在不对称染色体复制过程中，RecA对于稳定维持停滞在终点的复制叉以及它们最终独立于SOS和一些主要重组途径穿过终止屏障是必不可少的。
