A chick embryo fibroblast protein kinase recognizing ribosomal protein S6. Activity increase after serum stimulation

We sought protein kinase(ser) activity in DEAE-Sephacel chromatography fractions of the 10000 X g supernatants of chick embryo fibroblasts using 40 S ribosomal subunits as kinase substrate, and detected a new S6-recognizing kinase activity. There was one order of magnitude more enzyme activity in chromatography fractions derived from serum-stimulated than from serum-deprived cells. Known protein kinase regulators and a low dose tryptic treatment did not increase the enzyme's activity.