Ang JS, Duffy S, Segovia R, Stirling PC, Hieter P

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 catalogue of genome ...

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instability genes, we systematically explored the effects of gene over-expression on mutation rate, using a forward-mutation screen in budding yeast. We screened ~5100 plasmids, each over-expressing a unique single gene and characterized the five strongest mutators, MPH1, RRM3, UBP12, PIF1 and DNA2 We show that for MPH1, the yeast homolog of Fanconi Anemia complementation group M (FANCM), the over-expression mutator phenotype is distinct from that of mph1Δ. Moreover, while four of our top hits encode DNA helicases the over-expression of 48 other DNA helicases did not cause a mutator phenotype, suggesting this is not a general property of helicases. For Mph1 over-expression, helicase activity was not required for the mutator phenotype; in contrast Mph1 DEAH-box function was required for hypermutation. Mutagenesis by MPH1 over-expression was independent of translesion synthesis, but was suppressed by over-expression 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 up-regulation of DNA repair proteins may contribute to mutagenesis.

Date: Aug. 31, 2016

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