Effects of constitutively active PI3K and Rac2 on SCF-induced Rac activation. (A) fyn^−/−MSCV and fyn^−/−MSCV-Rac2^V12 BMMCs were activated with SCF for 0 or 5 minutes. CRIB pull-down assays were carried out to detect Rac2^GTP (endogenous and Myc-tagged) and total Rac2 in SCLs. Position of Myc-Rac2V12 is indicated by an open arrow on the left. (B) fyn^+/+ and fyn^−/− transduced with either MSCV or MSCV-p110^CAAX BMMCs were subjected to CRIB pull-down assays as described. Position of Rac2 is indicated on the left with an arrow.