Down-Regulation of Rad51 Activity during Meiosis in Yeast Prevents Competition with Dmc1 for Repair of Double-Strand Breaks

Abstract

Interhomolog recombination plays a critical role in promoting proper meiotic chromosome segregation but a mechanistic understanding of this process is far from complete. In vegetative cells, Rad51 is a highly conserved recombinase that exhibits a preference for repairing double strand breaks (DSBs) using sister chromatids, in contrast to the conserved, meiosis-specific recombinase, Dmc1, which preferentially repairs programmed DSBs using homologs. Despite the different preferences for repair templates, both Rad51 and Dmc1 are required for interhomolog recombination during meiosis. This paradox has recently been explained by the finding that Rad51 protein, but not its strand exchange activity, promotes Dmc1 function in budding yeast. Rad51 activity is inhibited in dmc1Δ mutants, where the failure to repair meiotic DSBs triggers the meiotic recombination checkpoint, resulting in prophase arrest. The question remains whether inhibition of Rad51 activity is important during wild-type meiosis, or whether inactivation of Rad51 occurs only as a result of the absence of DMC1 or checkpoint activation. This work shows that strains in which mechanisms that down-regulate Rad51 activity are removed exhibit reduced numbers of interhomolog crossovers and noncrossovers. A hypomorphic mutant, dmc1-T159A, makes less stable presynaptic filaments but is still able to mediate strand exchange and interact with accessory factors. Combining dmc1-T159A with up-regulated Rad51 activity reduces interhomolog recombination and spore viability, while increasing intersister joint molecule formation. These results support the idea that down-regulation of Rad51 activity is important during meiosis to prevent Rad51 from competing with Dmc1 for repair of meiotic DSBs.

Meiotic Recombination: The Essence of Heredity

“…Although the precise mechanism of this meiotic interhomolog bias remains unknown, coupling of recombination to homolog axes also provides a means for communication between sister chromatids to limit intersister recombination. In budding yeast, where interhomolog bias has been most clearly elucidated, an important aspect of interhomolog bias is modulation of the recombination complex by inhibiting Rad51 (which nonetheless retains an essential supporting role) and switching to Dmc1-mediated DNA pairing and strand exchange Niu et al 2009;Cloud et al 2012; Hong et al 2013;Lao et al 2013;Liu et al 2014b). Evidence suggests that this feature may be conserved, at least in Arabidopsis (Kurzbauer et al 2012;Da Ines et al 2013).…”

The Meiotic Checkpoint Network: Step-by-Step through Meiotic Prophase

“…Several mechanisms act in concert to achieve this goal, both by down-regulating sister-directed RAD51-recombinase activity and by promoting the homolog as the preferred repair template (Kim et al 2010;Lao and Hunter 2010;Kurzbauer et al 2012;Hong et al 2013;Lao et al 2013;Liu et al 2014). Research in a number of organisms indicates a central role of the MCN in establishing meiotic homolog bias (Carballo et al 2008;Latypov et al 2010), al-though the mechanistic details are best understood in S. cerevisiae (Fig.…”

Spontaneous self-segregation of Rad51 and Dmc1 DNA recombinases within mixed recombinase filaments

“…The reasons why eukaryotes have these two recombinases remain unknown (1,6). Rad51 and Dmc1 share ~45% amino acid identity (6,8,9), they assembly into structurally similar right-handed helical filaments on single-stranded DNA (ssDNA) (10)(11)(12), and they have similar, albeit not identical, biochemical properties (1,6). Despite these many commonalities, Dmc1 is the recombinase responsible for performing strand invasion during meiosis (13).…”

“…Despite these many commonalities, Dmc1 is the recombinase responsible for performing strand invasion during meiosis (13). In contrast, Rad51 is actively downregulated by Hed1-and Mek1-mediated inhibition of its interactions with Rad54, which is a cofactor that is required for Rad51 strand invasion activity (11,(14)(15)(16)(17). However, Rad51 is required for normal progression through meiosis and promotes Dmc1 foci formation, consistent with a role for Rad51 as a Dmc1 accessory factor (6,7,13,18).…”