Novel Cell Cycle-related Nuclear Proteins Found in Rat and Human Cells with Monoclonal Antibodies

Abstract Monoclonal antibodies which react specifically with the nuclei of interphase cells recognized three nuclear antigens with molecular weights of 110,000 (p110), 85,000 (p85), and 18,000 (p18). p110 and p85 were found in eight tumor cell lines but were not found in resting lymphocytes. p18 was found in resting lymphocytes as well as the tumor cell lines. Protein p85 appeared in phytohemagglutinin-stimulated lymphocytes in the G 1 phase and protein p110 appeared in the S phase. p110 and p85 were localized to the extranucleolar chromatin while p18 was distributed throughout the nucleus and was determined by microscopic and DNase digestion studies to be DNA associated. The anti-p110 antibody recognized a component of the DNA polymerase α 2 complex. Three novel nuclear proteins were identified using monoclonal antibodies. Two of these proteins (p110 and p85) are proliferating cell nuclear and nucleolar antigen-like while the third (p18) is not cell cycle dependent.