A nuclear casein type II kinase from maize endosperm phosphorylating HMG proteins.

A casein kinase of the type II was isolated and enriched from nuclear lysates of maize endosperm tissue. The kinase activity requires 10 mM Mg2+ for maximal activity, can utilize either ATP or GTP as phosphate donors and is inhibited by polyamines, heparin and monovalent cations. A substrate specificity of the kinase activity towards specific nuclear proteins is indicated by its phosphorylation of high mobility group (HMG) proteins isolated from endosperm and its lack of accepting histones as protein substrates.