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  • Both meiotic COs and NCOs require DNA synthesis current

    2021-02-26

    Both meiotic COs and NCOs require DNA synthesis, current data from sequencing also suggest that COs require more DNA synthesis than NCO 63., 64., 65.. However, analysis of the role of DNA synthesis in NCOs remains relatively uncharacterized. Emerging evidence points to a role for either Polδ or Polε in NCO formation. In yeast homologous recombination, Polδ, instead of Polε, as a major Mexiletine HCl is preferentially recruited to extend the 3’-end in a D loop 72., 73.. Researchers also observed post meiotic segregation (PMS) [60]. It is thought that PMS reflects the segregation of unrepaired heteroduplex DNA from meiosis. Another report demonstrated that DNA synthesis associated with DSBR in meiosis has a significantly lower accuracy than mitotic DNA replication 74., 75.. Together, these data suggest the mismatch repair or proofreading machinery may be inefficient in meiotic DSBR in plants. Because Polδ, rather than Polε, has a substantial role in both mismatch repair and proofreading 76., 77., it is more likely that Polε is used in NCO DSBR. Unfortunately, this does not provide an explanation for why the chromosome fragments observed in Polε and Mexiletine HCl Polδ mutants are less extensive than those observed in rad51, which is essential for all DSB repair. This discrepancy hints at other unknown DNA polymerases or functional redundancy among DNA polymerases involved in NCOs DNA synthesis.
    Conflict of interest
    Acknowledgments We apologize to colleagues whose work could not be cited owing to space constraints. J.H., H.M. and Y.W. are supported by the Ministry of Science and Technology of China (2011CB944603), the National Natural Science Foundation of China (31370347), and by funds from Fudan University and Rijk Zwaan. G.P.C. is supported by the US National Science Foundation (MCB1121563) and Rijk Zwaan.
    Introduction HR is a conserved pathway for the removal of DNA double strand breaks (DSBs) and the repair of injured DNA replication forks. Herein, a homologous DNA sequence is engaged by the processed lesion and serves as the template for DNA synthesis to initiate a usually error-free repair process (Jasin and Rothstein, 2013, Symington et al., 2014). Lesion processing entails nucleolytic resection of the 5′ DNA strand associated with a break end to generate a 3′-ended DNA tail of a considerable length (Daley, Niu, Miller, & Sung, 2015). The ssDNA tail is bound by the conserved recombinase enzyme Rad51 and its accessory factors, and the resulting nucleoprotein ensemble then searches for and engages the homologous locale either in the sister chromatid or in the homologous chromosome, followed by invasion of the latter to form a hybrid DNA joint called the displacement loop, or D-loop (Kowalczykowski, 2015, San Filippo et al., 2008). It should be noted that in the vast majority of eukaryotes, an additional, meiosis-specific recombinase called Dmc1 is needed for optimal interhomolog recombination (Brown and Bishop, 2014, Hunter, 2015), but here we focus on Rad51 only. Rad51 catalyzes D-loop formation within the context of a right-handed nucleoprotein filament known as the presynaptic filament, whose assembly requires ATP binding by Rad51, although ATP hydrolysis prompts the dissociation of Rad51 protomers from the DNA ligand (Sung, 1994). D-loop formation by the presynaptic filament is enhanced by associated factors including the Swi2/Snf2 family proteins Rad54 and Rdh54 and the ssDNA-binding protein RPA (Daley et al., 2014, Heyer, 2007). Following strand invasion, de novo DNA synthesis occurs within the D-loop. Several DNA polymerases (Pols), namely, Pol δ and Pol ɛ in yeast (Deem et al., 2011, Hicks et al., 2010, Maloisel et al., 2008) and Pol η in vertebrates (Buisson et al., 2014, Kawamoto et al., 2005, McIlwraith et al., 2005), have been proposed to contribute to DNA synthesis, and among them, Pol δ has emerged as the major player (Lydeard et al., 2007, Maloisel et al., 2008, Wilson et al., 2013). Following repair DNA synthesis, the extended D-loop is resolved via one of the several mechanistically distinct pathways to yield mature recombinants of different classes (Sung and Klein, 2006, Symington et al., 2014). The involvement of Pol δ in repair DNA synthesis has been studied most extensively within the context of a HR pathway called break-induced DNA replication (BIR), in which an invading DNA strand primes DNA synthesis capable of copying an entire arm of the donor chromatid (Fig. 1) (Costantino et al., 2014, Dilley et al., 2016, Donnianni and Symington, 2013, Lydeard et al., 2007, Saini et al., 2013, Wilson et al., 2013).