Abundant kinase activity of erk observed in cells with p210BCR-ABL or RafCAAX is independent of the presence of IL-3, whereas erk activity is induced in other cells by IL-3.

Lysates of the cells noted, taken either from IL-3–deprived or IL-3–stimulated cultures as noted, were immunoprecipitated with erk antibody, and the precipitate was subjected to immune complex kinase assay with MBP.