BubR1 checks in with CENP-E

A kinetochore protein plays both sides of the checkpoint field, according to Weaver et al. on page 551. They show that CENP-E, a mitotic checkpoint-silencing protein, also stimulates the amount of checkpoint inhibitor released from an unattached kinetochore.

The mitotic checkpoint is the major mechanism preventing chromosomal loss during mammalian mitosis. Unattached kinetochores generate an inhibitor that blocks the destruction of proteins whose loss is required for initiating chromosome segregation. The chromosomal kinesin CENP-E helps to silence checkpoint signaling by promoting stable bipolar kinetochore attachments to spindle pole microtubules. The checkpoint can be activated in the absence of CENP-E when most of the chromosomes are misattached (as occurs when microtubules are destabilized). But Weaver et al. show that if only one or two chromosomes are...