Tyrosine phosphorylation of Jaks in murine myeloid precursor cell lines. Two different murine myeloid precursor cell lines (FDC-P1, DA3) expressing wild type G-CSF receptor or NFS60 cells, which express the endogenous G-CSF receptor, were either unstimulated or stimulated with IL-3 (I) or G-CSF (G) for 5 minutes. Cells were lysed and incubated with antisera against either Jak1, Jak2, Jak3, or Tyk2, and immunoprecipitates were analyzed by Western blotting with a monoclonal antibody against phosphotyrosine (4G10).