yKu70-yKu80 overexpression suppresses GCR formation induced by different types of DNA damage or generated spontaneously. The increased GCR frequency was suppressed by the overexpression of the yKu70-yKu80 heterodimer in the presence of 0.1% MMS (A), 0.5 μg/ml bleomycin (Bleo) (B), and a single DSB introduced by an HO endonuclease (C). (D) Mcm1, a DNA binding protein, did not suppress the GCRs induced by MMS treatment. (E) GCR rates in different GCR mutator strains were reduced by Ku overexpression. Each GCR rate of a GCR mutator strain with control plasmids was recalculated to 100%, and the GCR rate with Ku overexpression was converted to a percentage compared with that of strains carrying control plasmids. 100% GCR rate presented here for rfa1-t33, mre11, rad27, and rfa1-t33 rad24 are 5.8 × 10−7, 5.9 × 10−7, 2.2 × 10−6, and 4.9 × 10−7, respectively. “+” and “−” represent the presence and absence of indicated proteins or the treatment and no treatment of indicated DNA damaging agents, respectively.