Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 1995 Nov 1;14(21):5399-409.
doi: 10.1002/j.1460-2075.1995.tb00224.x.

Preferential binding of human topoisomerase I to superhelical DNA

K R Madden  1 , L Stewart, J J Champoux
Affiliations

Preferential binding of human topoisomerase I to superhelical DNA

K R Madden et al. EMBO J. .

Abstract

Eukaryotic type I DNA topoisomerase provides swivels for removing torsional strain from the DNA helix during transcription and DNA replication. Previously it has been shown that the enzyme is associated with actively transcribed genes and replicating DNA. Using an inactive mutant form of the protein containing phenylalanine instead of tyrosine at position 723, we have investigated the binding properties of the protein as a function of substrate topology. A series of filter binding assays indicated that the protein strongly prefers to bind superhelical over completely relaxed SV40 DNA. The ability of a supercoiled DNA to compete against a relaxed DNA for binding increases as the number of superhelical turns in the DNA increases. Since positively supercoiled DNA is bound with the same preference as negatively supercoiled DNA, we hypothesize that topoisomerase I binds preferentially at the nodes created by the crossing of two duplex helices. The preference for binding superhelical DNA is also exhibited by the conserved core domain (amino acids 175-659) which is missing the active site region located near the C-terminus. These results suggest that this core domain may target the enzyme in vivo to regions of torsionally strained superhelical DNA.

PubMed Disclaimer

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Cancer Res. 1992 Feb 1;52(3):525-32 - PubMed
    1. Nucleic Acids Res. 1992 Jul 11;20(13):3347-52 - PubMed
    1. J Mol Biol. 1992 Oct 20;227(4):1224-43 - PubMed
    1. Proc Natl Acad Sci U S A. 1993 Apr 1;90(7):2759-63 - PubMed
    1. Nucleic Acids Res. 1993 Nov 11;21(22):5157-66 - PubMed

Publication types