The chromosomal passenger complex (CPC) consisting of INCENP, Survivin, Borealin and Aurora B kinase, plays crucial roles in mitosis and cytokinesis. The CPC localizes to chromosomes in early mitosis and to microtubules of the spindle midzone after anaphase onset. The mechanisms governing this dynamic localization are poorly understood. In particular, the factors ensuring CPC accumulation at the spindle midzone remain to be identified. In budding yeast, localization of INCENP to the central spindle require. Separase activation by the Cdk1antagonizing phosphatase Cdc14, but the function of mammalian Cdc14 paralogues in CPC regulation is less well defined. In human cells, the Mitotic kinesin-like protein-2 (Mklp2) binds both Aurora B and Cdc14 and is required for CPC and Cdc14 localization to the midzone. Recently, ubiquitination of CPC components was identified as a critical step regulating CPC localization during mitosis. Ubiquitination of Survivin promotes its association with centromeres during early mitosis but also triggers its dissociation from these structures at later mitotic stages. Moreover, we have shown that Cullin3 (Cul3) E3 ubiquitin ligases regulate CPC function during mitosis. Aurora B is ubiquitinated in vitro and potentially also in vivo by different Cul3 complexes formed with the substratespecific BTB-Kelch adaptors KLHL9, KLHL13 and KLHL21. Interestingly, Cul3/KLHL21, Cul3/KLHL9 and Cul3/ KLHL13 complexes mainly monoubiquitinate Aurora B in vitro. While polyubiquitination is primarily required Finding the midzone The role of ubiquitination for CPC localization during anaphase