Title

Regulation of the Aspergillus nidulans DNA damage response by UVSB and MUSN

Date of Completion

January 2001

Keywords

Biology, Molecular|Biology, Genetics|Biology, Microbiology

Degree

Ph.D.

Abstract

The survival of all cells is dependent on the accurate replication and faithful transmission of the genetic information during cellular reproduction. The DNA damage response is a multi-faceted response that coordinates the processes of DNA repair and cell cycle progression to enhance the cell's ability to maintain genomic integrity in the presence of spontaneous and induced DNA damage. Previous observations in the filamentous fungus Aspergillus nidulans had suggested that UVSB and UVSD were likely to control cell cycle checkpoint responses to DNA damage and incomplete replication. Consistent with this notion, we show here that UVSB is a member of the conserved family of PI-3K related kinases that includes Schizosaccharomyces pombe Rad3p, Saccharomyces cerevisiae Mec1p, and human ATM and ATR. We report that UVSB functions as a central regulator of the DNA damage response in Aspergillus nidulans, controlling several aspects of the response, including cell cycle arrest, inhibition of septum formation, induced mutagenesis, and possibly regulation of gene expression. ^ The musN227 mutation partially suppresses several of the defects caused by uvsB mutations, including the genotoxin sensitivity. We sought to understand the mechanism underlying this suppression by cloning the musN gene. Here, we report that musN encodes a RecQ-like helicase with homology to Schizosaccharomyces pombe rqh1, Saccharomyces 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. We propose a model in which MUSN functions to promote recovery from the DNA damage response. We suggest that the block to recovery caused by the musN227 mutation, coupled with the modest accumulation of recombination intermediates, can suppress defects caused by mutations in uvsB. ^ Finally, we report that Aspergillus nidulans possesses an additional RecQ helicase, ORQA, whose function partially overlaps with that of MUSN. Altogether, this work has revealed that studying the DNA damage response in Aspergillus nidulans may provide insight into the molecular basis of human genetic instability diseases and cancer susceptibility. ^