Elevation of intracellular casein kinase II (CKII) levels through microinjection of purified CKII results in the rapid and transient induction of c‐fos in quiescent rat embryo fibroblasts, and activation of quiescent cells by serum is accompanied by the nuclear relocation of endogenous CKII. The induction of c‐fos by CKII is inhibited by coinjection of oligonucleotides corresponding to the sequence of the serum response element (SRE) present in the c‐fos promoter, indicating that competitive displacement of positive factors from the endogenous c‐fos SRE prevents c‐fos induction by CKII. Furthermore, the expression of c‐fos induced by either CKII injection or serum activation is also inhibited by microinjection of antibodies against the 67 kDa serum response factor (p67SRF) indicating the absolute requirement of p67SRF in this process. Finally, we show the specific phosphorylation of p67SRF in vivo following microinjection of CKII into quiescent cells. Together, these data strongly support that CKII induces c‐fos expression through binding/activation of the phosphorylated p67SRF at the SRE sequence.

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It has been described that phosphorylation, and dephosphorylation, of specific proteins is associated with key events of the cell cycle and is likely to be due to activation of kinase(s). From our results, the presence of calcium-phospholipid-dependent protein kinase (PKC) was clearly demonstrated in both the cytosolic and particulate fractions of immature Xenopus laevis oocytes and in the cytosolic fraction of mature oocytes. However, it was less active in metaphase II-than in prophase I-arrested oocytes. The enzyme was partially purified by DEAE-cellulose and phenyl-Sepharose chromatography. It was activated in vitro by the tumorpromoting phorbol ester, 12-0tetradecanoyl phorbol 13-acetate (TPA) as already described for PKC from other tissues. On the other hand, a calcium-phospholipid-independent histone kinase activity 4-fold higher in metaphase II-than in prophase I-arrested oocytes was detected. The possible role of PKC and phospholipid-independent histone kinase in the maturation process is discussed.Protein kinase C; Tetradecanoyl phorbol acetate; Meiose; Oocyte; (Xenopus laevis)