Figure 4.
MKK7 is an activator of the JNK protein kinase in vivo. (A) CHO cells were cotransfected with epitope-tagged JNK1 together with an empty expression vector (Control) or an expression vector encoding MKK4 or MKK7. The JNK1 was isolated by immunoprecipitation using an HA monoclonal antibody, and the protein kinase activity was measured in the immunecomplex with [γ-32P]ATP and c-Jun as substrates. The product of the phosphorylation reaction was visualized after SDS/PAGE by autoradiography. (B) The cells were cotransfected with epitope-tagged p38 MAP kinase together with an empty expression vector (Control) or an expression vector encoding MKK6 or MKK7. The activity of p38α MAP kinase was examined in an immunecomplex kinase assay using ATF2 as the substrate. (C) The cells were cotransfected with epitope-tagged ERK2 together with an empty expression vector (Control) or an expression vector encoding MKK1 or MKK7. The activity of ERK2 was examined in an immunecomplex kinase assay using c-Myc as the substrate.