[Organization of microtubules and regulation of cell growth]

Microtubule organizing center is composed of a pair of centrioles and active pericentriolar materials. Its nucleating activity enhances at mitosis to organize a mitotic spindle. We raised a monoclonal antibody against microtubule associated protein 1. Indirect immunofluorescence by this antibody was located in the microtubule organizing center and in the nucleus. The intranuclear antigen was bound to the nuclear skeleton during interphase, and released to cytoplasm concentrating to the mitotic spindle and its poles. The nuclear immunofluorescence reversibly disappeared in growth-inhibited normal cells, but was always apparent in transformed cells.