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
. 1988 Dec 20;7(13):4355-65.
doi: 10.1002/j.1460-2075.1988.tb03334.x.

Assembly of spaced chromatin involvement of ATP and DNA topoisomerase activity

Affiliations

Assembly of spaced chromatin involvement of ATP and DNA topoisomerase activity

G Almouzni et al. EMBO J. .

Abstract

Undiluted extracts from eggs or oocytes of Xenopus laevis support the assembly of chromatin with physiologically spaced nucleosomes. Micrococcal nuclease and DNase I digestion experiments show that nucleosome formation as well as supercoiling of circular DNA concomitant to assembly do not require ATP or Mg2+. However these factors are essential for the stability and the physiological spacing of the assembled chromatin. gamma-S-ATP can substitute for ATP in this process. With topoisomers of defined linking number topological interconversions proceed by steps of unity, both in vitro as well as in vivo, indicating that topoisomerase I is dominantly acting in this process. Novobiocin sensitivity occurred only with diluted extracts and was unrelated to an inhibition of topoisomerase II. Finally, nucleosome assembly occurs efficiently on linear DNA although the assembled DNA is less stable than with circular DNA. From these results we propose that mature chromatin is formed in a two-step reaction. In the first step, nucleosome deposition occurs independently of ATP and Mg2+. Thus, nucleosome formation can be uncoupled from their spacing. In this step, topoisomerase activity is involved in the relaxation of the topological constraints generated by chromatin assembly rather than in the process of assembly itself. The second step, requiring ATP and Mg2+, generates properly spaced chromatin.

PubMed Disclaimer

Similar articles

Cited by

References

    1. Cell. 1976 Jul;8(3):333-47 - PubMed
    1. Proc Natl Acad Sci U S A. 1975 May;72(5):1843-7 - PubMed
    1. J Cell Sci. 1976 Nov;22(2):303-24 - PubMed
    1. Proc Natl Acad Sci U S A. 1976 Dec;73(12):4551-4 - PubMed
    1. J Embryol Exp Morphol. 1976 Dec;36(3):523-40 - PubMed

Publication types