PRC1: A human mitotic spindle-associated CDK substrate protein required for cytokinesis

We have identified a novel human protein, PRC1, that is involved in cytokin esis. PRC1 is a goad substrate for several CDKs in vitro and is phosphoryla ted in vivo at sites that are phosphorylated by CDK in vitro, strongly sugg esting that PRC1 is an in vivo CDK substrate, PRC1 has sequence homology to the budding yeast anaphase spindle Elongation factor Ase1p. Like Ase1p, PR C1 protein levels are high during S and G2/M and drop dramatically after ce lls exit: mitosis and enter G1. PRC1 is a nuclear protein in interphase, be comes associated with mitotic spindles in a highly dynamic manner during mi tosis, end localizes to the cell midbody during cytokinesis. Microinjection of anti-PRC1 antibodies into HeLa cells blocked cellular cleavage, hut not nuclear division, indicating a functional role for PRC1 in the process of cytokinesis.