| In this study , we have extended the analysis of these PKC beta transfectants to the mitogen activated protein kinase ERK 3 . ^^^ Analysis of cell lysates on the mitogen activated protein kinase substrate myelin basic protein by in gel kinase assay showed increased activity at 63 kDa , the size of ERK 3 , in each of two PKC beta 1 and each of two PKC beta 2 transfectants compared with the vector control transfectant . ^^^ ERK 3 was expressed at equal abundance in PKC beta 1 , PKC beta 2 , and control transfectant cells as demonstrated by Western blotting and by immunoprecipitation with anti ERK 3 monoclonal antibody . ^^^ However , a > 10 fold increase in ERK 3 activity in each PKC beta transfectant was shown by immunoprecipitation with anti ERK 3 monoclonal antibody followed by either immune complex kinase assay or by in gel kinase assay . ^^^ Thus , while overexpression of transfected PKC beta does not lead to overexpression of ERK 3 , it does lead to constitutive activation of ERK 3 . ^^^ |