Chromosomes in living Escherichia coli cells are segregated into domains of supercoiling.
Open Access
- 1 January 1981
- journal article
- research article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences
- Vol. 78 (1) , 224-228
- https://doi.org/10.1073/pnas.78.1.224
Abstract
Torsional tension in the DNA double helix can be detected in living cells of E. coli from measurements of the rate of trimethylpsoralen photobinding to the intracellular DNA. This tension is relaxed in vivo when single-strand DNA breaks are introduced by .gamma.-irradiation and that approximately 160 nicks/genome equivalent of DNA are required to relax > 95% of the tension. Chromosomes containing less than 160 nicks/genome equivalent lose only a part of the tension, depending on the number of nicks. The remaining tension is maintained during incubations of cells at 0.degree. C. Chromosomes with tension relaxed by incubation of cells with inhibitors of DNA gyrase interact with the trimethylpsoralen probe independently of the number of nicks introduced by .gamma.-irradiation. The results fit a model in which the chromosome in growing E. coli cells (mean generation time, 30 min) is segregated into 43 .+-. 10 domains of supercoiling/genome equivalent of DNA or 120 .+-. 30 domains/nucleoid. The number of domains is unchanged in cells depleted of nascent RNA by growth with rifampicin, but varies somewhat in cells growing at different rates in different media.Keywords
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