On the degree of unwinding of the DNA helix by ethidium. II. Studies by electron microscopy

Leroy-Fong Liu, James C. Wang

研究成果: 雜誌貢獻文章

56 引文 (Scopus)

摘要

When a negatively twisted covalently closed DNA is annealed with single-stranded fragments of the same DNA, under proper conditions a loop (or loops) may form by the disruption of a segment (or segments) of base pairs between the complementary strands of the covalently closed DNA, and the formation of base pairs between the strands of the covalently closed DNA and the single-stranded fragments. Since such a process involves essentially no net gain or loss of the number of base pairs, it is driven by the free energy favoring the reduction of the number of superhelical turns. If the fragments are sufficiently long or are present at a sufficiently high concentration during annealing, the most stable product between a covalently closed DNA and the DNA fragments (under conditions favoring the formation of double-stranded DNA) is a looped molecule devoid of superhelical turns. The size of the looped region or regions, which can be measured by electron microscopy, provides a way to determine the degree of superhelicity of the covalently closed DNA in the absence of the fragments. When this is compared with the degree of superhelicity of the covalently closed DNA determined by titration with the intercalative dye ethidium, the unwinding angle of the DNA double helix due to the intercalation of an ethidium can be calculated. Such measurements were done on two samples of phage PM2 DNA with different extents of supercoiling. The results are in agreement with the value 26° obtained recently by alkaline titration of covalently closed PM2 DNA samples in CsCl density gradients (Wang, J.C., (1974) J. Mol. Biol. 89, 783-801).

原文英語
頁(從 - 到)405-412
頁數8
期刊BBA Section Nucleic Acids And Protein Synthesis
395
發行號4
DOIs
出版狀態已發佈 - 七月 23 1975
對外發佈Yes

指紋

Electron Microscopy
DNA
Base Pairing
Ethidium
ethidium-DNA complex
Single-Stranded DNA
Bacteriophages
Coloring Agents

ASJC Scopus subject areas

  • Medicine(all)

引用此文

On the degree of unwinding of the DNA helix by ethidium. II. Studies by electron microscopy. / Liu, Leroy-Fong; Wang, James C.

於: BBA Section Nucleic Acids And Protein Synthesis, 卷 395, 編號 4, 23.07.1975, p. 405-412.

研究成果: 雜誌貢獻文章

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