FIG. 1.

ERF is phosphorylated in response to mitogens but not in response to stress. (A) Ref-1 cells expressing the ERF gene were arrested by serum starvation for 20 h and then induced for the indicated times with either 100 ng of epidermal growth factor (EGF) per ml or 25 ng of anisomycin (Anisom.) per ml. Thirty micrograms of cellular extract was analyzed by SDS gel electrophoresis, and proteins were detected by immunoblotting with the indicated antibodies. (B) Three hundred micrograms of the same cellular extracts was immunoprecipitated with anti-Erk or anti-JNK antibodies, as indicated. The kinase activity was detected by in-gel kinase assay with, as substrates, myelin basic protein (MBP) for Erks and the amino terminus of c-Jun for JNKs.