ASSOCIATION OF CASEIN KINASE-2 WITH NUCLEAR MATRIX - POSSIBLE ROLE INNUCLEAR MATRIX PROTEIN-PHOSPHORYLATION

The nuclear matrix is thought to play a fundamental role in the nuclea r structure and functions relating to cell proliferation and regulatio n of gene activity. Phosphorylation of nuclear matrix proteins has bee n observed, and multiple protein kinases may be involved in this proce ss. Casein kinase 2 is a ubiquitous messenger-independent serine/threo nine protein kinase that has been implicated in cellular growth and pr oliferation. The presence of immunoreactive casein kinase 2 in purifie d nuclear matrix preparations was demonstrated in rat liver and prosta te tissues by employing specific antibodies. The enzyme was active tow ard the specific decapeptide substrate Arg-Arg-Arg-Glu-Glu-Glu-Thr-Glu -Glu-Glu and exhibited other properties characteristic of casein kinas e 2. Phosphorylation of nuclear matrix proteins catalyzed by intrinsic protein kinase activity in intact nuclei was also observed, and the r esults suggested that this reaction was at least in part catalyzed by casein kinase 2. The profile of nuclear matrix proteins labeled with ( 32)p(i) in situ in intact liver cells was similar to that observed in nuclear matrix proteins isolated from nuclei labeled with [gamma-P-32] ATP in vitro. Association of casein kinase 2 with the nuclear matrix m ay be of significance in the post-translational modification of certai n proteins in this fraction.