Analysis of SUMOylation of topoisomerase IIalpha with Xenopus egg extracts.

Posttranslational protein modification by the Small Ubiquitin-like MOdifiers (SUMO) is involved in many cellular functions including organization of nuclear structures and chromatin, transcriptional regulation, and nucleo-cytoplasmic transport. Both genetic and biochemical studies indicate that the SUMO modification pathway plays an important role in proper cell cycle control, especially in the normal progression of mitosis. DNA topoisomerase II has been shown to be modified by SUMO in budding yeast as well as in vertebrates. We have shown by biochemical analysis using the Xenopus egg extract (XEE) cell-free assay system that DNA topoisomerase IIalpha (Topo IIalpha) is modified by SUMO-2/3 on mitotic chromosomes in the early stages of mitosis. Inhibition of mitotic SUMOylation in the XEE assay system causes aberrant sister chromatid separation in anaphase and alters Topo IIalpha association with chromosomes.