Fig. 8. Phosphorylation of p48 requires cytosolic components. Coomassie-stained SDS-PAGE gels (left) and autoradiograms (center) of equal aliquots of vesicles incubated with ³²P--ATP for the intervals indicated. Labeling of p48 (arrow) is barely detectable after 30 minutes incubation of vesicles alone but increases dramatically by 5 minutes after addition of cytosol. Incubation of cytosol alone in ³²P--ATP for 5 minutes yields almost no protein labeling.