At the end of cytokinesis, the dividing cells are connected by an intercellular bridge, containing the midbody along with a single, densely ubiquitylated circular structure called the midbody ring (MR). MRs are large (about 1.5 m), ring-like macromolecular assemblies that contain several proteins, including centriolin2, MKLP1 (ref. 7), the de-ubiquitylation enzyme USP8 (also known as UBPY)8, and the multifunctional anti-apoptotic ubiquitin ligase BRUCE3, 9, which has a relative molecular mass of 528,000 (Mr 528K).