Mapping of the constitutive binding domain of Vav1/2 on 3BP2. (A) Schematic structures of the 3BP2 mutants used in these experiments. The PH, proline-rich (PR), and SH2 domains are represented by black, white, and gray boxes, respectively. COS-1 cells were transiently cotransfected with expression plasmids encoding myc-tagged Vav1 (B) or Vav2 (C), and various HA-tagged 3BP2 mutant constructs. Immunoprecipitates were prepared with anti-HA antibody and probed with anti-myc antibody. The membranes were then stripped and reprobed with anti-HA antibody to control 3BP2 protein expression.