Leu278 at position −3 in the first SAP binding motif of CD150 partially stabilizes non–phosphotyrosine binding but is not required for phosphotyrosine-dependent interaction.

(A) Yeast 2-hybrid β-galactosidase assay for SAP/CD150 non–tyrosine phosphorylation–dependent interaction with CD150 or CD150 Lys276Asn or CD150 Leu278Ile. ▪, +SAP; ■, +pGBT9. (B) Altered yeast 2-hybrid using a modified Fyn (Fyn^{2YF R-Q}, see “Materials and methods” for details) to phosphorylate CD150. β-Galactosidase assay to measure strength of the SAP/CD150 interaction data are representative of 3 separate experiments. ▪, +SAP + Gyn^{2YF R-Q}; ■, +pBridge.