p31comet acts to ensure timely spindle checkpoint silencing subsequent to kinetochore attachment

• Published in: Molecular biology of the cell 2011-11, Vol.22 (22), p.4236-4246
• Main Authors: Hagan, Robert S., Manak, Michael S., Buch, Håkon Kirkeby, Meier, Michelle G., Meraldi, Patrick, Shah, Jagesh V., Sorger, Peter K., Doxsey, Stephen J
• Format: Article
• Language: eng ; jpn
• ISSN: 1059-1524; 1939-4586
• DOI: 10.1091/mbc.E11-03-0216

p31comet opposes the activities of the Mad2 spindle assembly checkpoint protein, localizes to unattached kinetochores, and like many checkpoint proteins, turns over rapidly at that site. Depletion of p31comet prevents timely passage into anaphase, showing that mitotic progression requires an active mechanism for silencing the spindle checkpoint. The spindle assembly checkpoint links the onset of anaphase to completion of chromosome-microtubule attachment and is mediated by the binding of Mad and Bub proteins to kinetochores of unattached or maloriented chromosomes. Mad2 and BubR1 traffic between kinetochores and the cytosol, thereby transmitting a “wait anaphase” signal to the anaphase-promoting complex. It is generally assumed that this signal dissipates automatically upon kinetochore-microtubule binding, but it has been shown that under conditions of nocodazole-induced arrest p31 comet , a Mad2-binding protein, is required for mitotic progression. In this article we investigate the localization and function of p31 comet during normal, unperturbed mitosis in human and marsupial cells. We find that, like Mad2, p31 comet traffics on and off kinetochores and is also present in the cytosol. Cells depleted of p31 comet arrest in metaphase with mature bipolar kinetochore-microtubule attachments, a satisfied checkpoint, and high cyclin B levels. Thus p31 comet is required for timely mitotic exit. We propose that p31 comet is an essential component of the machinery that silences the checkpoint during each cell cycle.