FIG. 1.
Identification of the 72-kDa Csk-associated phosphoprotein as G3BP. (A) Anti-PTyr immunoblots of material precipitated by a GST-Csk-SH3-SH2 protein (“before”). The second lane represents a parallel second sample, from which the region corresponding to the 72-kDa band was cut out with the help of the first lane, and the remaining filter was then blotted with anti-PTyr to verify that the correct band had been excised (“after”). The second filter is darker because it contained four times more material. (B) Mass spectrogram of the trypsin digest of the 72-kDa protein band from panel A. Peptide peaks derived from G3BP (✽) and trypsin (T) are indicated. (C) Anti-G3BP immunoblot of anti-Csk immunoprecipitates from untreated Jurkat T cells (lane 1) and from cells treated with OKT3 for 1 min (lane 2), 3 min (lane 3), 5 min (lane 4), or 10 min (lane 5). (D) Anti-G3BP immunoblot of anti-Csk immunoprecipitates from untreated normal human T lymphocytes (lane 1) and from cells treated with OKT3 and F(ab′)2 fragments for 2 min (lane 2), 5 min (lane 3), or 10 min (lane 4). The immunoglobulin heavy chain seen in lanes 2 to 4 is from OKT3.