FIG. 5.

JAK2 is autophosphorylated on tyrosines 221 and 570 in vivo. 293T cells expressing the cDNA for SH2-Bβ and JAK2 (A), JAK2 Y221F (B), or JAK2 Y570F (C) were incubated for 4 h in the presence of [³²P]orthophosphate. Cells were lysed, and JAK2 was immunoprecipitated using α-JAK2. [³²P]JAK2 was isolated and subjected to 2-D peptide mapping, with the TLE step performed at pH 3.5 (8).