Mind bomb I (Mib1) is a RING finger E3 ubiquitin ligase with few previously identified binding partners. Using a proteomics-based approach, this dissertation identifies several Mib1-associated proteins, including the plus-end–directed kinesin Eg5, and characterizes their functional interaction. Mib1 and Eg5 associate through the N-terminal region of Mib1, co-immunoprecipitate, and co-localize at the centrosome, where Mib1 promotes Eg5 monoubiquitination. Perturbation of either protein alters centrosome number, leading to centrosome amplification or suppression. Notably, Eg5 overexpression rescues Mib1-induced centrosome overproduction. These findings demonstrate that Mib1 and Eg5 act within a shared pathway to regulate centrosome number and maintain centrosome homeostasis.
