Excess Mph1p down-regulates HR. (A) High expression of Mph1p reduced mating type switching frequency using JKM161 with different plasmids (Δho HMLalpha MATa Δhmr:;ADE1 ade1-100 leu2-3,112 lys5 trp1∷hisg ura3-52 ade3∷GAL-HO endonuclease his-). (B) Excess Mph1p reduces the spontaneous recombination rate. (top) A schematic diagram of his3 inverted repeat spontaneous recombination assay using M137-11B with different plasmids (MATa can1-100 his3p∷INV leu2 lys2-128 trp1 ura3). (bottom) A graphic presentation of spontaneous recombination rates of cells carrying control (Ctrl) or Mph1p overexpression (o/e) plasmids. (C) GCR enhancement by excess Mph1p was completely blocked by Rad52p cooverexpression. (D) Excess Mph1p slowed down Rad51p recruitment to DSB. ChIP was performed using JKM161 with different plasmids. (E) Excess Mph1p made cells sensitive to γ irradiation and MMS. (F) Excess Mph1p made the dnl4Δ strain sensitive to MMS. (G) Strains carrying both mph1Δ and srs2Δ mutations showed synergistic sensitivity to MMS compared with strains carrying each single mutation. Rates are presented as the mean of two median values with standard deviation.