Kinase activity of Abl is necessary for the phosphorylation of CAP. HeLa cells were cotransfected with WT and mutants of CAP-EGFP and Abl. CAP was immunoprecipitated with GFP antibodies and the phosphorylation status was detected with anti-phospho-Tyr antibodies in Western blots. A: Full-length CAP was phosphorylated by Abl WT and Abl PP but not by Abl KD. B: WT CAP, all single WF and the 3xWF SH3 domain mutants were phosphorylated upon coexpression of c-Abl, whereas the CAPΔSH3 mutant was not.