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Updated: Aug 25, 2026

Quantitative Detection of DNA-Protein Crosslinks and Their Post-Translational Modifications
Published on: April 21, 2023
Identification of toposome, a novel multisubunit complex containing topoisomerase IIalpha
Chee-Gun Lee1, Lisa K Hague, Hong Li
1Department of Biochemistry and Molecular Biology, Graduate School of Biomedical Sciences, University of Medicine and Dentistry of New Jersey, Newark 07013, USA. leecg@umdnj.edu
Abstract:
Topoisomerase IIalpha plays essential roles in chromosome segregation. However, it is not well understood how topoisomerase IIalpha exerts its function during mitosis. In this report, we find that topoisomerase IIalpha forms a multisubunit complex, named toposome, containing two ATPase/helicase proteins (RNA helicase A and RHII/Gu), one serine/threonine protein kinase (SRPK1), one HMG protein (SSRP1), and two pre-mRNA splicing factors (PRP8 and hnRNP C). Toposome separates entangled circular chromatin DNA about fourfold more efficiently than topoisomerase IIalpha. Interestingly, this decatenation reaction yields knotted circles, which are not seen in reactions provided with monomeric circular DNA. Our results also show that interaction among toposome-associated proteins is highest in G2/M phase but drastically diminishes in G1/S phase. These results suggest that toposome is a dynamic complex whose assembly or activation is subject to cell cycle regulation.
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