DDB2 facilitates homologous recombination to repair IR-induced DSBs. a, b A549 and H1299 cells were transfected with DDB2 siRNA (a) and DDB2-expressing vectors (b), respectively. Cell were treated with IR and further cultured for the indicated time periods. Whole cell lysates were prepared and subjected to immunoblotting to detect DDB2 and phosphorylated H2AX (γH2AX). Actin was also detected as a loading control. c, d The HeLa cells stably transfected with pDR-GFP (HeLa-DR13–9 cells) were transfected with either control siRNA (siCtrl) or DDB2 siRNA (siDDB2) along with pCBASce plasmids for 3 days. GFP-positive cells were detected by flow cytometry. N = 3, bar: SD, **p < 0.01