(A) Cell cycle progression of stable knock-down HeLa clones after UVC (10 J/m2), γ rays (6 Gy) or etoposide treatment (VP16; 25 μM for 1.5 h): GG-NER and TC-NER pathways. Exponentially growing cells were treated and 24 h later adherent cells were collected, washed and fixed in 75% ethanol at 4°C for at least 24 h. Cells were stained with propidium iodide (4 μg/ml) in the presence of RNase (10 μg/ml) for at least 30 min. Stained cells were analyzed on a FACScalibur (Becton Dickinson) using CellQuest software. Here, ∼10 000 cells gated as single cells using FL2A/FL2W scatter were analyzed. Each clone was analyzed at least three times. Long-term HeLa clones: Control (BD650, day115), XPCKD (BD634/21; day 333), hHR23AKD (BD805/7; day 158), hHR23BKD (BD804/9; day 191), XPAKD (BD695/6; day 422). Arrows indicate a striking point highlighting intolerance to DNA damage. (B) NHEJ and HR pathways. Long-term HeLa clones: DNAPKcsKD (BD743/1; day 321), XRCC4KD (BD694/9; day 235), LigIVKD (BD940/3; day 103), LigIIIKD (BD941/11; day 82), Rad51KD (BD864/2; day 107), Rad54KD (BD912/5; day 148). (C) Signaling pathways Long-term HeLa clones: MRE11KD (BD930/32; day 61), Rad50KD (BD872/1; day 158), NBS1KD (BD932/11; day 108), ATMKD (BD935/12; day 111), ATRKD (BD962/9; day 56).