DNA damage-induced nuclear import of HSP90 alpha is promoted by Aha1

The interplay between yHSP90 alpha (Hsp82) and Rad51 has been implicated in the DNA double-strand break repair (DSB) pathway in yeast. Here we report that nuclear translocation of yHSP90 alpha and its recruitment to the DSB end are essential for homologous recombination (HR)-mediated DNA repair in yeast. The HsHSP90 alpha possesses an amino-terminal extension which is phosphorylated upon DNA damage. We find that the absence of the amino-terminal extension in yHSP90 alpha does not compromise its nuclear import, and the nonphosphorylatable-mutant HsHSP90 alpha(T7A) could be imported to the yeast nucleus upon DNA damage. Interestingly, the flexible charged-linker (CL) domains of both yHSP90 alpha and HsHSP90 alpha play a critical role during their nuclear translocation. The conformational restricted CL mutant yHSP90 alpha(Delta(211-259)), but not a shorter deletion version yHSP90 alpha(Delta(211-242)), fails to reach the nucleus. As the CL domain of yHSP90 alpha is critical for its interaction with Aha1, we investigated whether Aha1 promotes the nuclear import of yHSP90 alpha. We found that the nuclear import of yHSP90 alpha is severely affected in Aaha1 strain. Moreover, Aha1 is accumulated in the nucleus during DNA damage. Hence Aha1 may serve as a potential target for inhibiting nuclear function of yHSP90 alpha. The increased sensitivity of Aaha1 strain to genotoxic agents strengthens this notion.