Fission yeast Ase1^PRC1 is required for the G₂-microtubule damage response

Schizosaccharomyces pombe delays entry into mitosis following G₂ microtubule damage. This pathway is dependent on Rad26^ATRIP, the regulatory subunit of the Rad26^ATRIP/Rad3^ATR DNA damage response (DDR) complex. However, this G₂ microtubule damage response pathway acts independently of the G₂ DNA damage checkpoint pathway. To identify other proteins in this G₂ microtubule damage pathway, we previously screened a cDNA overexpression library for genes that rescued the sensitivity of rad26Δ cells to the microtubule poison thiabendazole. A partial cDNA fragment encoding only the C-terminal regulatory region of the microtubule bundling protein Ase1 ^PRC1 was isolated. This fragment lacks the Ase1^PRC1 dimerization and microtubule binding domains and retains the conserved C-terminal unstructured regulatory region. Here, we report that ase1Δ cells fail to delay entry into mitosis following G₂ microtubule damage. Microscopy revealed that Rad26^ATRIP foci localized alongside Ase1^PRC1 filaments, although we suggest that this is related to microtubule-dependent double strand break mobility that facilitates homologous recombination events. Indeed, we report that the DNA repair protein Rad52 co-localizes with Rad26^ATRIP at these foci, and that localization of Rad26^ATRIP to these foci depends on a Rad26^ATRIP N-terminal region containing a checkpoint recruitment domain. To our knowledge, this is the first report implicating Ase1^PRC1 in regulation of the G₂/M transition.