FIG. 7.

Mapping of the major tyrosine phosphorylation site in G3BP. (A) Tryptic peptide maps of G3BP or G3BP mutants phosphorylated in vitro by recombinant Lck as in Fig. 2C. The bottom right-hand panel is a schematic view of the major peptides and the spot that contains Y56. Note that this spot is missing in the maps of the Y56F and Y56F/Y125F mutants. A sample origin is indicated by an arrow. (B) The upper panel shows an anti-PTyr immunoblot of G3BP immunoprecipitated with the anti-HA epitope tag antibody from COS cells cotransfected with G3BP mutants and Lck or Fyn, as indicated. The lower panel shows equal amounts of G3BP in each lane verified by anti-HA immunoblotting of the same filter.