CtIP is phosphorylated by CDKs at multiple sites.

<p>A. Lysates from indicated cell lines were collected and treated with (+) or without (−) lambda phosphatase (ptase), followed by immunoblotting for endogenous CtIP. B. Schematic drawing of twelve putative CDK consensus sites (SP/TP motifs) on CtIP, with the middle cluster of sites 7A-CDK and 5A-CDK indicated. Myc-CtIP WT or indicated mutants were expressed in 293T cells, and cell lysates were treated with or without lambda phosphatase, followed by anti-Myc immunoblotting. C. and D. U2OS cells stably expressing HA-CtIP WT or indicated mutants with endogenous CtIP silenced, were treated with or without CPT (2 µM, 2 h) or IR (10 Gy, recovered for 1 h), followed by immunoblotting for anti-HA. E. Myc-BRCA1 and/or HA-CtIP WT or indicated mutants were expressed in 293T cells and co-immunoprecipitation was performed.