Comparison of nuclear nonhistone phosphoproteins of rat liver and Novikoff hepatoma.

As part of a continuing comparison of nuclear proteins of tumors and other tissues, 32P-labeled nuclear proteins were extracted successively with 0.15 and 0.35 m NaC1 from the nuclei of normal, regenerating, and thioacetamide-treated rat liver as well as Novikoff hepatoma 3 hr after injection of 32Pi into rats. Separation of proteins of these fractions with aqueous phenol was carried out before two-dimensional electrophoresis on polyacrylamide gels. By autoradiography many common spots were found, but four 32P-labeled protein spots, CU', C13p, C21p, and CMp, were found in the Novikoff hepatoma and not in the various liver samples studied. Two spots, B6 and B10, were found in the liver patterns and not in the tumor. Sot B33 was very dense in regenerating liver but was only a faint spot in thioacetamide-treated liver. The greater density of Spots CU', C13p, C21p, and CMp in the tumor patterns is consistent with the increased density reported earlier for spots of the C-region of a variety of tumors.