Thus, strand annealing for second end capture is a critical feature of both branches of the recombination pathway. But just as for COs, second end capture by strand annealing again occurs, with the released leading end being captured by the lagging DSB end to restore a non-exchange chromatid ( 20).

Among this branch of the pathway, it is the extended leading end that is released from the homolog partner, thus eliminating the interhomolog DNA connection (rather than the lagging end as for COs). NCO-designated intermediates also undergo extension of their 3′ tails, but without a discrete identifiable intermediate ( 15, 17). Further events ultimately yield double-Holliday junctions (dHJs) which are matured to COs ( 17, 20). Then, in a critical transition, the lagging DSB end is released from its sister association and reanneals with the extended leading end ssDNA, an event known as ‘second end capture’ ( 18, 19). The 3′ tail of the leading DSB end is then extended by DNA synthesis ( 1). For CO-designated intermediates, nascent D-loops first form a discrete long-lived ‘single end invasion’ intermediate (SEI) ( 10, 13–15, 17). A few interactions are designated to give evenly spaced crossovers (COs) while most of the remaining interactions giving rise to noncrossovers (NCOs) ( 3, 13–16). At this point, the recombination process bifurcates. The other end remains associated with its sister chromatid, likely also in nascent D-loop ( 10–12). One of these tails interacts with the corresponding sequence on a homolog partner chromatid, making a nascent D-loop. Recombination initiates by programmed double-strand breaks (DSBs) which undergo endo- and exo-nucleolytic resection of their 5′ ends to give long 3′ single stranded (ss) DNA tails ( 4–9). The DNA events of meiotic recombination, while elucidated primarily in budding yeast, are likely highly conserved across many organisms ( 1–3). These and other results imply a close correspondence between Rad52-RPA roles in meiotic recombination and mitotic DSB repair.ĭNA recombination is a central feature of meiosis and, thereby, sexual reproduction ( 1, 2). Our findings suggest that this spike represents the DSB end of a broken chromatid caused by either the displaced leading DSB end or the second DSB end, which has been unable to engage with the partner homolog-associated ssDNA. Furthermore, the absence of this Rad52-RPA joint activity results in a cytologically-prominent RPA spike, which emerges from the homolog axes at sites of crossovers during the pachytene stage of the meiotic prophase. Here, using physical analysis of DNA recombination, we demonstrate that this process is dependent on direct interaction of Rad52 with the ssDNA binding protein, replication protein A (RPA).

This second-end capture is dependent on Rad52, presumably via its known capacity to anneal two ssDNAs. Then, after regulated differentiation into crossover- and noncrossover-fated types, the second DSB end participates in the reaction by strand annealing with the extended first end, along both pathways. Studies in Saccharomyces cerevisiae have shown that, following rapid resection to generate 3′ single-stranded DNA (ssDNA) tails, one DSB end engages a homolog partner chromatid and is extended by DNA synthesis, whereas the other end remains associated with its sister.

Meiotic recombination is initiated by programmed double-strand breaks (DSBs).

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