Monoclonal antibody to a protein of the nucleus and mitotic spindle of mammalian cells. Localization and synthesis throughout the cell cycle.

We report here the isolation of a monoclonal antibody, J17, that reacts with a conserved vertebrate protein antigen that is present in the spindle apparatus during mitosis but found within the nucleus during interphase. Immunofluorescence microscopy demonstrates that the J17 antigen is found in numerous punctate regions that are distinct from nucleoli. Furthermore, this antigen is not directly associated with kinetochores, the nuclear envelope, or with metaphase chromosomes. Antibody J17 immunoprecipitates a single polypeptide of very high molecular weight (over 250 000) from K562 human erythroleukemia cells pulse-labeled with 14C-leucine. This polypeptide is converted quantitatively to a stable 220-kilodalton product within one cellular generation. We discuss the possible relevance of this processing event for transport into the nucleus. The J17 antigen is synthesized throughout the cell cycle in Chinese hamster ovary cells.