Nucleic Acids Research Advance Access originally published online on May 25, 2007
Nucleic Acids Research 2007 35(11):3810-3822; doi:10.1093/nar/gkm102
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Nucleic Acids Research, 2007, Vol. 35, No. 11 3810-3822
© 2007 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Molecular Biology |
C-Terminal regions of topoisomerase II
and IIß determine isoform-specific functioning of the enzymes in vivo
1Institute of Clinical Chemistry and Laboratory Diagnostics, Heinrich-Heine-University, Medical School, Moorenstrasse 5, D-40225 Düsseldorf, Germany and 2Gene Targeting Group, Department of Haematology, Imperial College Faculty of Medicine, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK
*To whom correspondence should be addressed. +49 211 8118036; +49 211 8118021; christensen{at}med.uni-duesseldorf.de
Received October 17, 2006. Revised January 23, 2007. Accepted February 6, 2007.
Topoisomerase II removes supercoils and catenanes generated during DNA metabolic processes such as transcription and replication. Vertebrate cells express two genetically distinct isoforms (
and ß) with similar structures and biochemical activities but different biological roles. Topoisomerase II is essential for cell proliferation, whereas topoisomerase IIß is required only for aspects of nerve growth and brain development. To identify the structural features responsible for these differences, we exchanged the divergent C-terminal regions (CTRs) of the two human isoforms ( 1173-1531 and ß 1186-1621) and tested the resulting hybrids for complementation of a conditional topoisomerase II knockout in human cells. Proliferation was fully supported by all enzymes bearing the CTR. The CTR also promoted chromosome binding of both enzyme cores, and was by itself chromosome-bound, suggesting a role in enzyme targeting during mitosis. In contrast, enzymes bearing the ß CTR supported proliferation only rarely and when expressed at unusually high levels. A similar analysis of the divergent N-terminal regions ( 1-27 and ß 1-43) revealed no role in isoform-specific functions. Our results show that it is the CTRs of human topoisomerase II that determine their isoform-specific functions in proliferating cells. They also indicate persistence of some functional redundancy between the two isoforms.