G-CSF–induced tyrosine phosphorylation of Jaks in the fibrosarcoma cell lines. Whole cell extracts from the indicated cells, with or without treatment for 5 minutes at 37°C with G-CSF, were immunprecipitated with anti-Tyk2, anti-Jak1, or anti-Jak2 polyclonal antibodies. Precipitated proteins were separated by SDS-PAGE, transferred to nitrocellulose, and probed with antibodies to phosphotyrosine (α-PTyr). Subsequently, filters were stripped and reprobed with Tyk2, Jak1, or Jak2 polyclonal antibodies.