Casein kinase II activity of buffalo sperm chromatin

Two cyclic AMP-independent protein kinase activities have been found associated with buffalo sperm chromatin: a histone kinase highly specific for arginine-rich histone was reported recently (Mudgal et al., 1997: Arch Andrology 38:191-199) and a casein kinase II is described here. Casein kinase activity was solubilized with 0.35 M NaCl, which extracted 90% of the initial enzyme activity associated with buffalo sperm chromatin. Of the two acidic proteins tested, casein was preferred substrate over phosvitin. Among the casein fractions, the order of preference for casein kinase was beta-casein > alpha-casein > casein. Cyclic AMP at concentrations up to 50 microM had no effect on the phosphorylation of casein. Phosphoamino acid analysis using casein as the substrate showed threonine to be the acceptor amino acid for phosphoester link. Phosphorylation specificity was determined by phosphorylating buffalo beta-casein followed by the preparation of tryptic peptides and identification of amino acid residue phosphorylated. Threonine residue at position 41 having clusters of acidic amino acid residues (Thr. Glu. Asp. Glu) C-terminal to it was phosphorylated, a phosphorylation specificity akin to CKII. It is thought that phosphorylation of histones decreases their association with DNA and probably makes the DNA more available for replication, while phosphorylation of nonhistone proteins modifies their interaction with histones, allowing control of template activity. Two protein kinases found in buffalo sperm chromatin may perform a similar function.