Nuclear Pores Protect Genome Integrity by Assembling a Premitotic and Mad1-Dependent Anaphase Inhibitor

The spindle assembly checkpoint (SAC) delays anaphase until all chromosomes are bioriented on the mitotic spindle. Under current models, unattached kinetochores transduce the SAC by catalyzing the intramitotic production of a diffusible inhibitor of APC/CCdc20 (the anaphase-promoting complex/cyclosome and its coactivator Cdc20, a large ubiquitin ligase). Here we show that nuclear pore complexes (NPCs) in interphase cells also function as scaffolds for anaphase-inhibitory signaling. This role is mediated by Mad1-Mad2 complexes tethered to the nuclear basket, which activate soluble Mad2 as a binding partner and inhibitor of Cdc20 in the cytoplasm. Displacing Mad1-Mad2 from nuclear pores accelerated anaphase onset, prevented effective correction of merotelic errors, and increased the threshold of kinetochore-dependent signaling needed to halt mitosis in response to spindle poisons. A heterologous Mad1-NPC tether restored Cdc20 inhibitor production and normal M phase control. We conclude that nuclear pores and kinetochores both emit “wait anaphase” signals that preserve genome integrity. [Display omitted] •Mad1-Mad2 directs mitotic checkpoint complex (MCC) assembly during interphase•Interphase MCC assembly requires Mad1’s nuclear-pore-targeting domain and Tpr•Loss of interphase MCCs reduces mitotic timing, fidelity, and checkpoint robustness•Artificially tethering Mad1-Mad2 to nuclear pores restores normal M phase controls A newly identified interphase checkpoint to prevent premature anaphase involves the tethering of checkpoint proteins Mad1-Mad2 to nuclear pores. This checkpoint is important for reinforcing the kinetochore-based checkpoint that kicks in after nuclear envelope breakdown as disabling it accelerates anaphase and increases chromosome segregation errors.