FIG. 8.

Syk-induced phosphorylation of R1 and CD8Δ-R1 chimeras. (A) Phosphorylation of R1 in vitro. An in vitro kinase assay was performed using extracts from Cos-1 cells transfected with R1 alone or in combination with Syk and Src kinase. Immune complexes were washed extensively and subsequently incubated with [γ-³²P]ATP. Complexes were then separated by gel electrophoresis and exposed to autoradiography. Arrow, presence of a 70 kDa phosphorylated protein that corresponds to the molecular sizes of both Syk and R1. (B) Tyrosine phosphorylation of CD8Δ-R1 chimeras induced by Syk kinase. Cos-1 cells were cotransfected with a Syk expression plasmid along with the CD8Δ-R1 chimera-expressing plasmids. The chimeras were tagged with an anti-AU1 antibody. Immunoprecipitations (I.P.) were performed using an anti-AU1 antibody and an anti-pTyr antibody was used for a Western blot analysis (I.B.). Dots, positions of mutant proteins.