Identification of a Nucleolin Binding Site in Human Topoisomerase I

doi:10.1074/jbc.271.4.1993

Identification of a Nucleolin Binding Site in Human Topoisomerase I (*)

From the (1)Division of Cancer Pharmacology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115 and the
(2)Department of Biochemistry, The University of Mississippi Medical Center, Jackson, Mississippi 39216

^§ To whom correspondence should be addressed:
UMDNJ-Robert Wood Johnson Medical School, Dept. of Pharmacology and The Cancer Institute of New Jersey, 675 Hoes Ln., Piscataway, NJ 08854-5635.

Abstract

DNA topoisomerase I (topo I) is involved in the regulation of DNA supercoiling, gene transcription, and rDNA recombination. However, little is known about interactions between topo I and other nuclear proteins. We used affinity chromatography with a topo I fusion protein to screen U-937 leukemic cell extracts and have identified nucleolin as a topo I-binding protein. Coimmunoprecipitation and other studies demonstrate that the interaction between topo I and nucleolin is direct. Furthermore, deletion analyses have identified the 166-210-amino acid region of topo I as sufficient for the interaction with nucleolin. Since nucleolin has been implicated in nuclear transport and in a variety of transcriptional processes, the interaction with topo I may relate to the cellular localization of topo I or to the known role of this topoisomerase in transcription.

Footnotes

↵*This work was supported by United States Public Health Service Grants CA70981 (to E. H. R.) and CA19589 (to D. W. K.), awarded by NCI, National Institutes of Health, and GM28349 (to M. O. J. O.), awarded by NIGMS, National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

topo I

topoisomerase I

PBS

phosphate-buffered saline

PAGE

polyacrylamide gel electrophoresis

NLS

nuclear localization sequence

GST

glutathione S-transferase.
- Received August 23, 1995.
- Revision received November 17, 1995.