In vertebrate cells, the small ubiquitin-like modifier SUMO plays a poorly defined role in targeting DNA topoisomerase II (TopoII) to centromeres (CENs) during mitosis, presumably to facilitate the untangling of sister chromatids as cells transition into anaphase. A new study by Dawlaty in the April 4 issue of Cell identifies the nucleoporin RanBP2 as a novel tumor suppressor that acts as a SUMO ligase for TopoII. Analysis of this interaction reveals TopoII recruitment to CENs is likely to play an important role in preventing chromosome segregation errors that lead to cancer.
