Fig. 7. The ability of IEX-1 to stimulate ERK activity is specific and requires its DEF motif. (A) CHO cells were transfected with HA-IEX-1 together with HA-JNK1 or empty vector (V) and treated or not for 10 min with 100 ng/ml anisomycin. Activated JNK was detected in anti-HA immunoprecipitates by immunoblotting with anti-phospho-JNK antibodies and by in vitro kinase assay using GST–c-jun as substrate. (B and C) CHO cells were transfected with HA-ERK, along with either empty vector (V), plasmids encoding the indicated HA-IEX-1 species or HA-Elk1. ERK activity was determined in anti-HA immunoprecipitates by in vitro kinase assay.