Project description:Genetic recombination generates novel trait combinations, and understanding how recombination is distributed across the genome is key to modern genetics. The PRDM9 protein defines recombination hotspots; however, megabase-scale recombination patterning is independent of PRDM9. The single round of DNA replication, which precedes recombination in meiosis, may establish these patterns; therefore, we devised an approach to study meiotic replication that includes robust and sensitive mapping of replication origins. We find that meiotic DNA replication is distinct; reduced origin firing slows replication in meiosis, and a distinctive replication pattern in human males underlies the subtelomeric increase in recombination. We detected a robust correlation between replication and both contemporary and historical recombination and found that replication origin density coupled with chromosome size determines the recombination potential of individual chromosomes. Our findings and methods have implications for understanding the mechanisms underlying DNA replication, genetic recombination, and the landscape of mammalian germline variation.
Project description:DNA damage tolerance (DDT) is crucial for genome integrity maintenance. DDT is mainly carried out by template switch recombination, an error-free mode of overcoming DNA lesions, or translesion DNA synthesis, which is error-prone. Here we investigated the role of Mgs1/WRNIP1 in modulating DDT. Using budding yeast, we found that elimination of Mgs1 in cells lacking Rad5, an essential protein for DDT, activates an alternative mode of DNA damage bypass, driven by recombination, that allows chromosome replication and cell viability under stress conditions that block DNA replication forks. This salvage pathway is RAD52- and RAD59-dependent, requires the DNA polymerase and PCNA-modification at K164, and is enabled by Esc2 and the PCNA-unloader Elg1, being inhibited when Mgs1 is present. We propose that Mgs1 is necessary to prevent a potentially toxic recombination salvage pathway at sites of perturbed replication, which in turn favors Rad5-dependent template switching, thus helping to preserve genome stability.
Project description:DNA duplication is intimately connected to setting up post-replicative chromosome structures and events, but molecular details of this coordination are not well understood. A striking example occurs during yeast meiosis, where replication locally influences timing of the DNA double-strand breaks (DSBs) that initiate recombination. We show here that replication-DSB coordination is eliminated by overexpressing Dbf4-dependent Cdc7 kinase (DDK) or removing Tof1 or Csm3, components of the replication fork protection complex (FPC). DDK physically associates with Tof1, and Tof1 is dispensable for replication-DSB coordination if DDK is artificially tethered to replisomes. Furthermore, DDK phosphorylation of the DSB-promoting factor Mer2 is locally coordinated with replication, dependent on Tof1. These findings indicate that DDK recruited by FPC to replisomes phosphorylates chromatin-bound Mer2 in the wake of the replication fork, thus synchronizing replication with an early prerequisite for DSB formation. This may be a general mechanism to ensure spatial and temporal coordination of replication with other chromosomal processes. Ninety-six samples total: 12 time points (each time points contains ChIP and input samples) from Rec114-myc ARS+, Rec114-myc arsM-bM-^HM-^F strains, Rec114-myc tof1M-bM-^HM-^FARS+ and Rec114-myc tof1M-bM-^HM-^F arsM-bM-^HM-^F strains
Project description:Accurate completion of replication relies on the ability of cells to activate error-free recombination-mediated DNA damage-bypass at sites of perturbed replication. However, as anti-recombinase activities are also recruited to replication forks, how recombination-mediated damage-bypass is enabled at replication stress sites remained puzzling. Here we uncovered that the conserved SUMO-like domains-containing Saccharomyces cerevisiae protein, Esc2, facilitates recombination-mediated DNA damage tolerance by allowing optimal recruitment of the Rad51 recombinase specifically at sites of perturbed replication. Mechanistically, Esc2 binds stalled replication forks and counteracts the anti-recombinase Srs2 helicase via a two-faceted mechanism involving chromatin recruitment and turnover of Srs2. Importantly, point mutations in the SUMO-like domains of Esc2 that reduce its interaction with Srs2 cause sub-optimal levels of Rad51 recruitment at damaged replication forks. In conclusion, our results reveal how recombination-mediated DNA damage tolerance is locally enabled at sites of replication stress, while globally prevented at undamaged replicating chromosomes.
Project description:During gamete formation, crossover recombination must occur on replicated DNA to ensure proper chromosome segregation in the first meiotic division. We identified a Mec1/ATR-dependent replication checkpoint in budding yeast that prevented the earliest stage of recombination, the programmed induction of DNA double-strand breaks (DSBs), when pre-meiotic DNA replication was delayed. The checkpoint suppressed DSBs through three complementary mechanisms: inhibition of Mer2 phosphorylation by Dbf4-dependent Cdc7 kinase, preclusion of chromosomal loading of Rec114 and Mre11, and lowered abundance of the Spo11 nuclease. Without this checkpoint, cells formed DSBs on partially replicated chromosomes. Importantly, such DSBs frequently failed to be repaired and impeded further DNA synthesis, leading to a rapid loss in cell viability. We conclude that a checkpoint-dependent constraint of DSB formation to duplicated DNA is critical not only for meiotic chromosome assortment, but also to protect genome integrity during gametogenesis. DSB factor association was measured in wild-type and checkpoint mutants strains under non-inducing or replication checkpoint inducing conditions. Additionally, DNA replication and helicase loading were measured in a replication and checkpoint deficient strain (cdc6-mn).