CHARACTERIZATION OF THE ENDOGENOUS PROTEIN-KINASE ACTIVITY OF THE HEPATITIS-B VIRUS

During the assembly of the nucleocapsid of the hepatitis B virus a pro tein kinase, probably of cellular origin, is encapsidated. This enzyme phosphorylates serine residue(s) localized within the lumen of the pa rticle. By using purified, liver-derived core particles, we characteri zed the protein kinase activity in the presence of different ions and inhibitors. Controls were performed with cAMP-dependent protein kinase (PKA) and protein kinase C (PKC) and recombinant core particles. We s howed that the endogenous protein kinase of the core particles was not inhibited by H89, a specific inhibitor of PKA. Staurosporine, a selec tive inhibitor of PKC inhibited the endogenous kinase activity only wi thin the first minutes of the reaction. In contrast, quercetine, a sel ective inhibitor of the protein kinase M (PKM) did not inhibit during the first minutes but inhibited efficiently during later phases of inc ubation. PKM represents an enzymatically active proteolytic fragment o f PKC. These results suggest that PKC is encapsidated into human core particles and is converted to PKM during the in vitro reaction. This c onclusion implies the association of a protease activity localized wit h the HBV nucleocapsid inside liver-derived core particles.