Gap filling during postreplication repair of DNA in recombination deficient Escherichia coli

RuvABC Is Required to Resolve Holliday Junctions That Accumulate following Replication on Damaged Templates in Escherichia coli

“…Several of these studies proposed related models that suggested that strand exchanges may be involved in the repair or tolerance of lesions that are skipped over by the replication machinery and would require resolution of Holliday junctions at a late step in this repair process (1,20,21). Although the early steps in these processing pathways remain to be identified, the observations presented here are consistent with a role for RuvABC in resolving strand exchanges after replication has occurred.…”

“…Consistent with this type of model, elevated levels of recombination-dependent strand exchanges are observed in repair-deficient mutants during the period when the nascent strand gaps are joined (1,20,21). However, experimentally, daughter strand gap repair has been characterized in repair-deficient populations under conditions where high levels of strand exchanges are observed (1,20,21). The high levels of lethality under these conditions make it dif-ficult to determine the precise efficiency at which this process is able to promote survival (1).…”

“…Then, at various times during the recovery period, the relative size of the 14 C-labeled genomic DNA and 3 H-labeled postirradiation DNA synthesis was determined by sedimentation in alkaline sucrose gradients. A large body of work by a number of investigators has shown that the limited DNA synthesis that occurs after irradiation is made up of small fragments containing gaps that are subsequently restored (or filled in) during the recovery period (1,8,9,20,21). Consistent with this, immediately following UV irradiation, the 3 H-labeled postirradiation DNA synthesis produced smaller sized fragments that migrated more slowly and separated from the large 14 Clabeled genomic DNA at the bottom of the gradient.…”

“…Early models proposed that the nascent strand gaps may be restored by exchanging and then resynthesizing these regions with the homologous regions of sister chromosomes (8,9). Consistent with this type of model, elevated levels of recombination-dependent strand exchanges are observed in repair-deficient mutants during the period when the nascent strand gaps are joined (1,20,21). However, experimentally, daughter strand gap repair has been characterized in repair-deficient populations under conditions where high levels of strand exchanges are observed (1,20,21).…”

“…5, we have presented a model to help clarify that differential repair of arresting and nonarresting lesions may occur to hopefully help resolve what appears to be conflicting observations from early studies (1,2,20,21). Although it is well documented that UV-induced lesions can arrest DNA replication, a large number of studies have found that a limited amount of gapped DNA synthesis can still be detected after UV irradiation, suggesting that not all lesions result in the arrest of DNA replication (1,2,20,21). The model we have presented suggests that replication fork reactivation downstream of the damaged DNA results in a gap opposite to the site of damage FIGURE 5.…”