Similar to ubiquitin, Small Ubiquitin-like Modifiers (SUMOs) can form polymers. However, the identity of the target proteins that are conjugated to these SUMO polymers was largely unknown. Using a proteomics approach that combined SUMO-enrichment with inactivation of the key SUMO polymer protease SENP6, a set of 180 of these targets have now been found. This set includes nearly all constitutive centromere associated network (CCAN) components. In the absence of SENP6, CCAN components CENP-T and CENP-W failed to properly accumulate at centromeres, indicating that the removal of SUMO polymers from these proteins is essential for their proper subcellular localization. Reduced accumulation of CCAN components resulted in delayed mitosis and subsequent formation of micronuclei. Interestingly, SUMO polymers on CCAN components didn’t target them for degradation, indicating that SUMO polymers have a more diverse signalling function than previously anticipated.
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