The kinetics of XRCC1 foci in the BRCA1-deficient breast cancer cell line MDA-MB-436 are similar to those in U2OS cells and are also sensitive to niraparib treatment (Supplementary Figure S2F and G), suggesting that BRCA1 does not directly modulate the PAR–dependent, early recruitment of XRCC1. The gene discussed is BRCA1; the disease is breast cancer.