Fission Yeast Ase1 is Required for the G-microtubule Damage Response

delays entry into mitosis following G microtubule damage. This pathway is dependent on Rad26, the regulatory subunit of the Rad26/Rad3 DNA damage response (DDR) complex. However, this G microtubule damage response pathway acts independently of the G DNA damage checkpoint pathway. To identify other proteins in this G microtubule damage pathway, we previously screened a cDNA overexpression library for genes that rescued the sensitivity of cells to the microtubule poison thiabendazole. A partial cDNA fragment encoding only the C-terminal regulatory region of the microtubule bundling protein was isolated. This fragment lacks the Ase1 dimerization and microtubule binding domains and retains the conserved C-terminal unstructured regulatory region. Here, we report that cells fail to delay entry into mitosis following G microtubule damage. Microscopy revealed that Rad26 foci localized alongside Ase1 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 at these foci, and that localization of Rad26 to these foci depends on a Rad26 N-terminal region containing a checkpoint recruitment domain. To our knowledge, this is the first report implicating Ase1 in regulation of the G/M transition.