RAFTK activation upon chemokine stimulation. Total cell lysates from L1.2 or CCR5-L1.2 cells unstimulated (UN) or stimulated with MIP1β (25 nmol/L) were immunoprecipitated with RAFTK antibody. The immune complexes were subjected to (A) autophosphorylating activity or (B) in vitro kinase assays using poly (Glu/Tyr, 4:1) substrate. The³²P-incorporated proteins were resolved on 7.5% SDS-PAGE followed by autoradiography. Both autokinase and total kinase activity were increased upon stimulation of the CCR5-L1.2 cells with MIP1β.