A 32-kD GTP-binding protein associated with the CD4-p56 super(lck) and CD8-p56 super(lck) T cell receptor complexes

The guanosine triphosphate (GTP)-binding proteins include signal-transducing heterotrimeric G proteins (for example, G sub(s), G sub(i)), smaller GTP-binding proteins that function in protein sorting, and the oncogenic protein p21 super(ras). The T cell receptor complexes CD4-p56 super(lck) and CD8-p56 super(lck) were found to include a 32- to 33-kilodalton phosphoprotein (p32) that was recognized by an antiserum to a consensus GTP-binding region in G proteins. Immunoprecipitated CD4 and CD8 complexes bound GTP and hydrolyzed it to guanosine diphosphate (GDP). The p32 protein was covalently linked to ( alpha - super(32)P)GTP by ultraviolet photoaffinity labeling.