The Aspergillus nidulans musN gene encodes a RecQ helicase that interacts with the PI-3K-related kinase UVSB.

In Aspergillus nidulans, the uvsB gene encodes a member of the PI-3K-related kinase family of proteins. We have recently shown that UVSB is required for multiple aspects of the DNA damage response. Since the musN227 mutation is capable of partially suppressing defects caused by uvsB mutations, we sought to understand the mechanism underlying the suppression by cloning the musN gene. Here, we report that musN encodes a RecQ helicase with homology to S. pombe rqh1, S. cerevisiae sgs1, and human BLM and WRN. Phenotypic characterization of musN mutant alleles reveals that MUSN participates in the response to a variety of genotoxic agents. The slow growth and genotoxin sensitivity of a musN null mutant can be partially suppressed by a defect in homologous recombination caused by the uvsC114 mutation. In addition, we present evidence suggesting that MUSN may promote recovery from the DNA damage response. We suggest that a block to recovery caused by the musN227 mutation, coupled with the modest accumulation of recombination intermediates, can suppress defects caused by uvsB mutations. Finally, we report that another RecQ helicase, ORQA, performs a function that partially overlaps that of MUSN.