RECEPTOR-BINDING, TYROSINE PHOSPHORYLATION AND CHROMOSOME LOCALIZATION OF THE MOUSE SH2-CONTAINING PHOSPHOTYROSINE PHOSPHATASE SYP

The murine phosphotyrosine phosphatase, Syp, is a widely-expressed cyt oplasmic enzyme that contains two SH2 domains. Syp is physically assoc iated with activated receptors for epidermal growth factor (EGF) and p latelet-derived growth factor (PDGF), apparently through its SH2 domai ns. This phosphatase is rapidly phosphorylated in cells treated with P DGF or EGF, and is constitutively phosphorylated in v-src transformed cells. Here we report that either the N-terminal or C-terminal Syp SH2 domain alone bound to the activated beta PDGF receptor or EGF-recepto r in vitro, and that the two SH2 domains linked together exhibited syn ergistic binding. Substitution of the Tyr1009 autophosphorylation site in the C-terminal tail of activated beta PDGFR with Phe abolished the in vitro binding of either SH2 domain to the activated receptor. A 9 amino acid phosphopeptide corresponding to the Tyr1009 autophosphoryla tion site of the beta PDGFR inhibited association of the Syp SH2 domai ns with the receptor. These results indicate that the Syp SH2 domains have an intrinsic specificity for the Tyr1009 autophosphorylation site of the beta PDGFR that dictates binding of the intact Syp phosphatase , and suggest that both SH2 domains have a related binding specificity . Phosphoamino acid analysis of Syp from PDGF-stimulated cells indicat ed that PDGF primarily induces Syp phosphorylation on tyrosine residue s. The mouse Syp gene has been mapped to chromosome 5F region by the f luorescence in situ hybridization. These findings suggest specific fun ctions for Syp in signal transduction downstream of receptor tyrosine kinases.