Jak2 can phosphorylate Tec at Tyr-518. (A) The kinase-dead Tec^KM (T^M) was expressed in 293 cells either alone or in combination with Jak2 (Jak2) or Lyn (Lyn) kinase. Tec was immunoprecipitated from each fraction, and probed with anti-phosphotyrosine antibody (αP-Tyr) or anti-Tec serum (αTec). (B) Tec^KM (T^M), Tec^KM▵SH3 (T^M▵3), or Tec^KM,YF (T^M,518F) was expressed in 293 cells either alone (−) or in combination with Jak2 (J) or Lyn (L). Tec was immunoprecipitated from each fraction, and blotted with anti-phosphotyrosine antibody (αP-Tyr) or anti-Tec serum (αTec). The positions of full-length Tec (T) and SH3-deleted (▵SH3) forms are indicated at the right. (C) The amino acid sequences of the Tec-family kinases, surrounding the tyrosine residues corresponding to Tyr-518 in mouse Tec, are compared. The asterisk indicates the position of the phosphorylated tyrosine. At the left shown are the numbers of amino acid positions of mouse Tec,2 human Btk,10,11 mouse Emt/Itk/Tsk, ^9,41,42 human Bmx,43 and human Txk.⁴⁴ (D) pSRα (V), pSRα-Tec (T), or pSRα-Tec^KM (T^M) was transfected into 293 cells with or without pSRα-Jak2 (J). Tec was immunoprecipitated from each fraction, and incubated with [γ−³²P]ATP without exogenous substrates. Autophosphorylation of pp70^Tec in each sample is shown.