FIG. 2.
Activation of ERK MAP kinase by hSos1 truncation mutants. COS1 cells were transiently cotransfected with HA-tagged ERK2 (0.5 μg) and the indicated HA-tagged hSos1 constructs. ERK2 activation was measured in serum-starved cells by immune complex kinase assay using MBP as a substrate. (Upper) MBP phosphorylation as visualized by autoradiography. The amount of 32P incorporated into MBP was determined by phosphorimaging and is indicated under each lane in arbitrary units. Results shown are from a single representative experiment. Experiments were repeated three times with similar results. (Lower) Immunoblot with anti-HA antibody showing the level of expression of ERK2.