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. 1980 Mar;77(3):1331-5.
doi: 10.1073/pnas.77.3.1331.

Supercoils in prokaryotic DNA restrained in vivo

D E Pettijohn, O Pfenninger

Supercoils in prokaryotic DNA restrained in vivo

D E Pettijohn et al. Proc Natl Acad Sci U S A. 1980 Mar.

Abstract

Cells of Escherichia coli containing the plasmid F were gamma-irradiated with various doses to introduce determined numbers of single-strand breaks in the F DNA. The cells were then incubated to permit repair of the breaks while DNA gyrase was inhibited with coumermycin to limit restoration of any relaxed supercoil. Repaired, covalently continuous F DNA was isolated and its superhelical density was measured by two different methods. Both indicated that a major part (50-60%) of the negative superhelical turns were maintained in the repaired molecules, suggesting that the supercoils are restrained in vivo.

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