Courcelle J, Hanawalt P C
Department of Biological Sciences, Mississippi State University, P.O. Box GY, Mississippi State, MS 39762-5759, USA.
Proc Natl Acad Sci U S A. 2001 Jul 17;98(15):8196-202. doi: 10.1073/pnas.121008898.
Alternative reproductive cycles make use of different strategies to generate different reproductive products. In Escherichia coli, recA and several other rec genes are required for the generation of recombinant genomes during Hfr conjugation. During normal asexual reproduction, many of these same genes are needed to generate clonal products from UV-irradiated cells. However, unlike conjugation, this latter process also requires the function of the nucleotide excision repair genes. Following UV irradiation, the recovery of DNA replication requires uvrA and uvrC, as well as recA, recF, and recR. The rec genes appear to be required to protect and maintain replication forks that are arrested at DNA lesions, based on the extensive degradation of the nascent DNA that occurs in their absence. The products of the recJ and recQ genes process the blocked replication forks before the resumption of replication and may affect the fidelity of the recovery process. We discuss a model in which several rec gene products process replication forks arrested by DNA damage to facilitate the repair of the blocking DNA lesions by nucleotide excision repair, thereby allowing processive replication to resume with no need for strand exchanges or recombination. The poor survival of cellular populations that depend on recombinational pathways (compared with that in their excision repair proficient counterparts) suggests that at least some of the rec genes may be designed to function together with nucleotide excision repair in a common and predominant pathway by which cells faithfully recover replication and survive following UV-induced DNA damage.
交替的生殖周期利用不同策略来产生不同的生殖产物。在大肠杆菌中，Hfr 接合过程中产生重组基因组需要 recA 和其他几个 rec 基因。在正常的无性繁殖过程中，从紫外线照射的细胞产生克隆产物也需要许多相同的基因。然而，与接合不同的是，后一过程还需要核苷酸切除修复基因的功能。紫外线照射后，DNA 复制的恢复需要 uvrA、uvrC 以及 recA、recF 和 recR。基于在缺乏 rec 基因时新生 DNA 会发生广泛降解这一情况，rec 基因似乎是保护和维持停滞在 DNA 损伤处的复制叉所必需的。recJ 和 recQ 基因的产物在复制恢复之前处理受阻的复制叉，并且可能影响恢复过程的保真度。我们讨论了一个模型，其中几种 rec 基因产物处理因 DNA 损伤而停滞的复制叉，以促进通过核苷酸切除修复来修复阻断性 DNA 损伤，从而使连续复制能够恢复，而无需进行链交换或重组。依赖重组途径的细胞群体的低存活率（与切除修复能力强的对应群体相比）表明，至少一些 rec 基因可能被设计为与核苷酸切除修复一起在一个共同且主要的途径中发挥作用，通过该途径细胞在紫外线诱导的 DNA 损伤后能够忠实地恢复复制并存活。
