Abstract: Nuclear pore complexes (NPCs) correspond to large protein transport complexes responsible for selective nucleocytoplasmic exchange. Although research has revealed much about the molecular architecture and roles of the NPC subcomplexes, little is known about the regulation of NPC functions by posttranslational modifications. We used a systematic approach to show that more than half of NPC proteins were conjugated to ubiquitin. In particular, Nup159, a nucleoporin exclusively located on the cytoplasmic side of the NPC, was monoubiquitylated by the Cdc34/SCF (Skp1-Cdc53-F-box E3 ligase) enzymes. Preventing this modification had no consequences on nuclear transport or NPC organization but strongly affected the ability of Nup159 to target the dynein light chain to the NPC. This led to defects in nuclear segregation at the onset of mitosis. Thus, defining ubiquitylation of the yeast NPC highlights yet-unexplored functions of this essential organelle in cell division.