In meiosis, efficient repair of programmed double-strand breaks (DSBs) is crucial for genome integrity and faithful chromosome segregation. We identified RAD-54.B as factor important for normal survival following radiation exposure, and we are investigating its functions during meiotic prophase. RAD-54.B is a member of the SNF-2/SWI-2 ATPase/helicase protein family, and its paralog RAD-54.L is essential for repair of meiotic DSBs. Whereas
rad-54.L mutants exhibit 100% progeny lethality, reflecting failure to remove recombinase RAD-51 from processed meiotic DSBs and failure to form post-strand-exchange recombination intermediates,
rad-54.B mutants exhibit nearly wild-type (WT) progeny viability, reflecting successful formation of crossovers (COs) between homologous chromosomes. However, there are two notable abnormal features of the meiotic program in
rad-54.B mutants. First,
rad-54.B mutants exhibit hyperaccumulation of RAD-51 foci during the early pachytene stage. Despite highly elevated levels of chromosome-associated RAD-51, however, post-strand-exchange recombination intermediates marked by MSH-5 occur with timing and numbers comparable to WT, and in contrast to
rad-54.L mutants, transition to the late pachytene stage occurs with normal timing in a
rad-54.B mutant and is accompanied by disappearance of hyperaccumulated RAD-51. Second, CO distribution as assayed genetically is altered in a
rad-54.B mutant; however, cytological measurement of positions of late pachytene COSA-1 foci along chromosome axes suggest that CO designation and CO interference are normal. Immunofluorescence analysis reveals that endogenously-tagged RAD-54.B::GFP localizes to chromosome-associated foci in early pachytene, sometimes colocalizing with markers of inter-homolog recombination intermediates; RAD-54.B::GFP foci diminish in number upon exit from early pachytene and are absent from CO-designated sites in late pachytene. We are currently testing the hypothesis that RAD-54.B antagonizes association of RAD-51 with unbroken double-stranded DNA, a function that RAD-54.L may be able to carry out if meiotic DSBs are absent. In addition, we hypothesize that RAD-54.B also functions at meiotic DSB repair sites in cooperation and/or competition with RAD-54.L to influence the structure of DSB repair intermediates and repair outcomes. (*KY and BW contributed equally)