Characterization of casein kinase II, and of p98 as one of its effective phosphate acceptors in sea urchin eggs

Abstract

CK-II has been partially purified from a 1.5 M KCl extract of unfertilized sea urchin eggs by means of DEAE-cellulose column chromatography, gel filtration on Sephacryl S300, and heparin-agarose column chromatography, successively. This partially purified CK-II was associated with a 98 kDa polypeptide (designated as p98), which was then separated from the kinase by Mono Q column chromatography (HPLC). The biochemical characteristics of CK-II purified from unfertilized eggs were similar to those of CK-IIs from various mammalian cells: requirements of divalent cations (Mg2+ and Mn2+) and phosphate acceptors (casein and p98), response to basic polypeptides and heparin, subunit structure and molecular size. Moreover, it was found that: (i) p98 (apparent pI 10.0) has DNA-binding ability and functions as an effective phosphate acceptor for CK-II in vitro; (ii) phosphorylation of p98 by the kinase was highly stimulated by histone-like sperm protein from sea urchin sperm, protamine (salmon sperm), and poly Arg; and (iii) selective phosphorylation of p98 by CK-II was detected when the DEAE-cellulose fraction from unfertilized eggs was incubated with [gamma-32P]ATP in the presence of protamine. Some biochemical characteristics of p98 from the eggs were similar to those of transcriptional factor Sp1. The evidence obtained suggests that (i) arginine-rich sperm proteins function as potent activators for CK-II in unfertilized eggs and (ii) specific phosphorylation of p98 by the activated kinase may play an important role in the transcriptional regulation in the eggs accompanying fertilization.