Figure 6.

BRCA1 is dispensable for HC-DSB repair while combined loss of BRCA1, 53BP1 and KAP-1 allows DSB repair by HR. (A, B) A549 cells were exposed to 3 Gy IR and γH2AX foci enumerated in G1 and G2 cells with or without siRNA BRCA1 and KAP-1. G2 and G1 cells were identified as in Figure 1. Results shown used a single BRCA1 oligonucleotide; identical results were obtained using a distinct pool of oligonucleotides. Aphidicolin was added as previously described. (C–E) A549 cells were treated with the indicated siRNAs, exposed to 3 Gy IR and examined for RPA (C), RAD51 (D) or γH2AX (E) foci at the indicated times. Results are shown in samples with or without siRNA KAP-1 to expose the necessity to have relaxed HC to observe HR in G2 phase. The k.d efficiency following multiple siRNA transfection is shown in Supplementary Figure S1. Results represent the mean and s.d. of three experiments. The statistical significance was determined using Student’s t-test. Asterisks indicate P < 0.05.