Srs2 helicase prevents the formation of toxic DNA damage during late prophase I of yeast meiosis

Abstract

Proper repair of double-strand breaks (DSBs) is key to ensure proper chromosome segregation. In this study, we found that the deletion of the SRS2 gene, which encodes a DNA helicase necessary for the control of homologous recombination, induces aberrant chromosome segregation during budding yeast meiosis. This abnormal chromosome segregation in srs2 cells accompanies the formation of a novel DNA damage induced during late meiotic prophase-I. The damage may contain long stretches of single-stranded DNAs (ssDNAs), which lead to aggregate formation of a ssDNA binding protein, RPA, and a RecA homolog, Rad51, as well as other recombination proteins inside of the nuclei. The Rad51 aggregate formation in the srs2 mutant depends on the initiation of meiotic recombination and occurs in the absence of chromosome segregation. Importantly, as an early recombination intermediate, we detected a thin bridge of Rad51 between two Rad51 foci or among the foci in the srs2 mutant, which is rarely seen in wild type. These might be cytological manifestation of the connection of two DSB ends and multi-invasion. The DNA damage with Rad51 aggregates in the srs2 mutant is passed through anaphase-I and -II, suggesting the absence of DNA damage-induced cell-cycle arrest after the pachytene stage.We propose that Srs2 helicase resolves early protein-DNA recombination intermediates to suppress the formation of aberrant lethal DNA damage during late prophase-I.

S. cerevisiaeSrs2 helicase ensures normal recombination intermediate metabolism during meiosis and prevents accumulation of Rad51 aggregates

“…Previous studies had shown that loss of Srs2 activity causes delays and defects in meiotic nuclear division, as well as reduced sporulation and spore viability (Palladino and Klein, 1992;Sasanuma et al, 2013b). Our current study and an accompanying study (Sasanuma et al, 2019) have identified recombination abnormalities in meiosis I prophase that are likely the cause of abnormal nuclear division in srs2 mutants.…”

“…The observation of persistent Rad51 aggregates in srs2 mutants (Figure 4; Sasanuma et al, 2019) suggests that Srs2 has a similar function during meiosis. Interestingly, while aggregate formation does not require progression through meiosis I (Sasanuma et al, 2019), the absence of aggregates from ndt80∆ mutants, and from NDT80 cells with foci or linear arrays of the SC protein Zip1 (Figs. 5b and 6; Sasanuma et al, 2019), indicates that Rad51 aggregates do not form until cells have exited from pachytene and disassembled SC.…”

“…S2a, Fig. 4, Sasanuma et al (2019)], indicating that abnormal recombination intermediates are a likely cause. A minority of srs2 mutant cells (21-27%) do not divide their nuclei (Fig.…”

“…Srs2 is thought to disrupt or prevent formation of Rad51containing nucleoprotein filaments during the mitotic cell cycle (Niu and Klein, 2017). The observation of persistent Rad51 aggregates in srs2 mutants (Figure 4; Sasanuma et al, 2019) suggests that Srs2 has a similar function during meiosis. Interestingly, while aggregate formation does not require progression through meiosis I (Sasanuma et al, 2019), the absence of aggregates from ndt80∆ mutants, and from NDT80 cells with foci or linear arrays of the SC protein Zip1 (Figs.…”

“…Interestingly, while aggregate formation does not require progression through meiosis I (Sasanuma et al, 2019), the absence of aggregates from ndt80∆ mutants, and from NDT80 cells with foci or linear arrays of the SC protein Zip1 (Figs. 5b and 6; Sasanuma et al, 2019), indicates that Rad51 aggregates do not form until cells have exited from pachytene and disassembled SC. Rad51 strand exchange activity is inhibited before pachytene exit (Subramanian et al, 2016), and Rad51 aggregate formation is greatly reduced in srs2 rad51-II3A mutants (Fig.…”