title: Dosage Mutator Genes in Saccharomyces cerevisiae: A Novel Mutator Mode-of-Action of the Mph1 DNA Helicase.
abstract: Mutations that cause genome instability are considered important predisposing events that contribute to initiation and progression of cancer. Genome instability arises either due to defects in genes that cause an increased mutation rate (mutator phenotype), or defects in genes that cause chromosome instability (CIN). To extend the catalog of genome instability genes, we systematically explored the effects of gene overexpression on mutation rate, using a forward-mutation screen in budding yeast. We screened ∼5100 plasmids, each overexpressing a unique single gene, and characterized the five strongest mutators, MPH1 (mutator phenotype 1), RRM3, UBP12, PIF1, and DNA2 We show that, for MPH1, the yeast homolog of Fanconi Anemia complementation group M (FANCM), the overexpression mutator phenotype is distinct from that of mph1Δ. Moreover, while four of our top hits encode DNA helicases, the overexpression of 48 other DNA helicases did not cause a mutator phenotype, suggesting this is not a general property of helicases. For Mph1 overexpression, helicase activity was not required for the mutator phenotype; in contrast Mph1 DEAH-box function was required for hypermutation. Mutagenesis by MPH1 overexpression was independent of translesion synthesis (TLS), but was suppressed by overexpression of RAD27, a conserved flap endonuclease. We propose that binding of DNA flap structures by excess Mph1 may block Rad27 action, creating a mutator phenotype that phenocopies rad27Δ. We believe this represents a novel mutator mode-of-action and opens up new prospects to understand how upregulation of DNA repair proteins may contribute to mutagenesis.
authors: Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
authors: J Sidney
authors: JS
authors: Ang
authors: Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
authors: Supipi
authors: S
authors: Duffy
authors: Terry Fox Laboratory, BC Cancer Agency, Vancouver, British Columbia V5Z 1L3, Canada.
authors: Romulo
authors: R
authors: Segovia
authors: Terry Fox Laboratory, BC Cancer Agency, Vancouver, British Columbia V5Z 1L3, Canada.
authors: Peter C
authors: PC
authors: Stirling
authors: Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada hieter@msl.ubc.ca.
authors: Philip
authors: P
authors: Hieter
mesh_terms: D053487:DEAD-box RNA Helicases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism; D045585:Flap Endonucleases / Q000235:genetics / Q000378:metabolism; D059645:Mutation Rate; D011485:Protein Binding; D000072417:Protein Domains; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D029701:Saccharomyces cerevisiae Proteins; D045585:Flap Endonucleases; C468323:RAD27 protein, S cerevisiae; C491240:MPH1 protein, S cerevisiae; C085463:PIF1 protein, S cerevisiae; C459081:Rrm3 protein, S cerevisiae; D004265:DNA Helicases; C410222:DNA2 protein, S cerevisiae; D053487:DEAD-box RNA Helicases
keywords: Mph1; forward mutation; genome-wide; mutator; overexpression