PRKK Activates SIMK, MMK3, and SAMK in Vivo.
MBP kinase activities of immunoprecipitated SIMK-HA, MMK2, MMK3-HA, and SAMK when expressed transiently in protoplasts alone (lane 2), with active MAPKKK ΔNPK1 (lane 5), with SIMKK (lane 3), or with PRKK in the absence (lane 4) or presence (lane 6) of ΔNPK1. Protoplasts transformed with the empty vector pRT101 were used as a negative control (lane 1). MAPK activity was analyzed by MBP phosphorylation of immunoprecipitated SIMK-HA, MMK2, MMK3-HA, and SAMK. After SDS-PAGE, MAPK activities were determined by autoradiography (A) and MAPK expression levels were assessed by immunoblotting with HA, MMK2, or SAMK antibody (B).