BUB-3 and SAN-1/MAD3 Spindle Assembly Checkpoint Components Are Required for Genome Stability in Response to Treatment with Ionizing Radiation.

Relatively little is known about the cross-talk between the spindle assembly checkpoint and the DNA damage response, especially in multicellular organisms. We performed a forward genetic screen to uncover new genes involved in the repair of DNA damage induced by ionizing radiation. We isolated a mutation, , which confers hypersensitivity to ionizing radiation and showed that introduces a premature stop in BUB-3 is a key component of the spindle assembly checkpoint. We provide evidence that BUB-3 acts during development and in the germline; irradiated () larvae are developmentally retarded and form abnormal vulvae. Moreover, () embryos sired from irradiated worms show increased levels of lethality. Both and (the homolog of MAD3) deletion alleles confer hypersensitivity to ionizing radiation, consistent with the notion that the spindle assembly checkpoint pathway is required for the DNA damage response. () is moderately sensitive to the cross-linking drug cisplatin but not to ultraviolet light or methyl methanesulfonate. This is consistent with a role in dealing with DNA double-strand breaks and not with base damage. Double mutant analysis revealed that does not act within any of the three major pathways involved in the repair of double-strand breaks. Finally, the gain-of-function mutant (), which is refractory to the cell cycle delay conferred by the spindle checkpoint, showed phenotypes similar to and mutants. We speculate that BUB-3 is involved in the DNA damage response through regulation of cell cycle timing.