Constitutively active Lck enhances tyrosine phosphorylation of VP11/12 in Vero cells. Vero cells were transfected with plasmids encoding constitutively active Y505F Lck, VP11/12, and a VP11/12-GFP fusion protein, as indicated. Cell lysates were collected 46 h posttransfection. Phosphotyrosine, GFP, and β-actin were detected by Western blotting. In all figures, the numbers on the left are molecular size markers (in kilodaltons).