DNA-binding sperm proteins with oligo-arginine clusters function as potent activators for egg CK-II.

The stimulatory effect of DNA-binding sperm proteins (histone and protamine) on the phosphorylation of p98 (ERp99/GRp94, one of the Hsp-90 family of proteins) by egg casein kinase II (CK-II) was investigated in vitro. It was found that (i) phosphorylation of p98 by egg CK-II in vitro is greatly stimulated by poly-Arg, but not by poly-Lys; and (ii) similar stimulation is observed with sperm histones H2B2 and H2B3 (sea urchin) and fish protamines, such as salmine A1 (salmon) and protamine 3a (rainbow trout). These findings suggest that these DNA-binding sperm proteins function as potent activators for CK-II in fertilized eggs. All of these DNA-binding sperm proteins contain at least an oligo-Arg cluster as a common feature, which can interact with an acidic amino acid cluster of the regulatory beta-subunit CK-II.