As ATM phosphorylates hundreds of substrates52, it may be that it operates at multiple, other levels11 to prevent NHEJ and ensure HRR of broken replication forks.
Restart of a broken replication fork that has generated a seDSB (as is the case upon topotecan or olaparib treatment) requires HRR using the homologous sister chromatid as template.
This result argues that the DNA lesions that initiate mitotic recombination are a consequence of chromosome breakage in unreplicated DNA, contrary to the common belief that most recombinogenic lesions reflect broken replication forks.
However, in the presence of CPT, Cds1 is dispensable when cells restore broken replication forks (Figure 5A).
In this condition, rad3Δ cells were able to recover broken replication forks more efficiently than swi3Δ cells (Figure 5C).
These results suggest that the replication checkpoint function of Swi3 does not have a major role in the recovery of broken replication forks induced by CPT.
WRN is implicated in telomere preservation by resolving alternate structures at telomeres during replication, and by restoring stalled or broken replication forks [10], [33].
It is possible that Swi1 Swi3 facilitates efficient repair of broken replication forks, although further investigation is needed to address this possibility.
This elongation was similar to that of swi3Δ and swi1Δ cells (Figure 4C), suggesting that Class I mutant cells experience severe difficulty in recovering broken replication forks.
In addition, recent evidence from yeast suggests that broken replication forks may also be substrates for an HR-protein independent, replication-based template-switching mechanism that is mediated by microhomology or microsatellites [9].
cds1Δ cells failed to show significant defects in replication recovery after CPT exposure, indicating that Cds1 does not have a major role in the recovery of broken replication forks.
