1. A B 1.2 1.2 1 1 0.8 0.8 Relative RNA level / control Relative RNA level / control *** *** ** *** *** * 0.6 0.6 0.4 0.4 0.2 0.2 0 0 DNA-PKcsKD DNA-PKcsKD DNA-PKcsKD CtKD CtKD CtKD CtKD CtKD CtKD Rad51KD Rad51KD Rad51KD HeLa As3WT2 HCT116 HeLa As3WT2 HCT116 C 1.2 1 0.8 Relative RNA level / control * *** 0.6 0.4 0.2 0 CtKD DNA-PKcsKD Rad51KD HeLa H2B-GFP Supp Fig. 1

2. siDNA-PKcs siCt siRad51 0 Gy HeLa 6 Gy 0 Gy As3wt2 6 Gy 0 Gy HCT116 6 Gy Cell count DNA content Supp Fig. 2

3. 20 15 10 5 0 CtKD CtKD CtKD Rad51KD Rad51KD Rad51KD DNA-PKcsKD DNA-PKcsKD DNA-PKcsKD 20 A Spontaneous chromatid breaks (%) B 15 Spontaneous chromosome breaks (%) 10 5 0 CtKD CtKD CtKD Rad51KD Rad51KD Rad51KD DNA-PKcsKD DNA-PKcsKD DNA-PKcsKD HeLa As3wt2 HCT116 Supp Fig. 3