And-1 antibody was obtained from Novus (#NBP1-89091, dilution: 1:500 for WB and 1:100 for IF). BRCA1 (D-9, dilution: 1:100 for IF, Santa Cruz) and (C-20, 1:200 for WB and IP, Santa Cruz), HA (H9658, dilution: 1:1000 for WB and IP, Sigma), FLAG (F3165, dilution: 1:1000 for WB and IP, Sigma), γH2AX (05-636, dilution: 1:500 for IF, Millipore), CtIP (61141, dilution: 1:500, Active Motif) for IF and (sc-28324, dilution 1:11 000) for WB, Chk1 (sc-7898, dilution: 1:1000 for WB, Santa Cruz), and P-Chk1-317 (2344S, 1:500 for WB, Cell Signaling), MDC1 (ab11171, 1:500 for IF), NBS1(ab32074, 1:200 for IF) were used. Antibodies against RPA, RAD51 and 53BP1 were previously described (47 (link)–49 (link)). And-1 full-length was subcloned from pEFF-And-1(a kind gift from Dr Zhu) (44 (link)) into the FLAG-tagged vector (pIRES2-EGFP) and HA-tagged vector (pCMV-HA) and GFP-tagged vector (pFUGW). And-1 deletion mutants were generated by site-directed mutagenesis and confirmed by sequencing. Full-length CtIP and D1–D6 deletion mutants were kindly provided by Dr Chen (50 (link)).