Binding of CRKL to ABL in the yeast two-hybrid system. ABL and BCR-ABL constructs and a lamin control were expressed as LexA-fusion proteins and analyzed for interaction with CRKL and CRK II expressed as VP-16 acidic activation domain fusion proteins. Two additional VP-16 constructs, AAP1 and AAP2, that were identified in our yeast two-hybrid screen using the ABL kinase domain were used as controls. + indicates positivity for β-galactosidase activity and growth on his− plates. Abbreviations: ABL-WT refers to the SH2, kinase construct depicted in Fig 1; ABL-KD is a kinase defective version of ABL; P1, P2, are the deletion mutants of the proline-rich regions depicted in Fig 1.