Physiological Levels of Salt and Polyamines Favor Writhe and Limit Twist in DNA

• Type of Material: Article
• Authors: Qing Shao, Emory University; Sachin Goyal, Emory University; Laura Finzi, Emory University; David Dunlap, Emory University
• Language: English
• Date: 2012-04-10
• Publisher: AMER CHEMICAL SOC
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2012 American Chemical Society.
• Final Published Version (URL): http://dx.doi.org/10.1021/ma300211t
• Title of Journal or Parent Work: MACROMOLECULES
• Volume: 45
• Issue: 7
• Start Page: 3188
• End Page: 3196
• Grant/Funding Information: This work was supported by National Institutes of Health (5R01GM084070-03 to LF); the Human Frontier Science Program (RGP0051/2009 to DD); and the University Research Council at Emory University (to DD).
• Keywords: ENTROPIC ELASTICITY; Science & Technology; Physical Sciences; BINDING; CONFORMATION; SINGLE-MOLECULE; B-Z TRANSITION; SPERMINE; MECHANICS; TOPOISOMERASES; DYNAMICS; RODS; Polymer Science
• Research Categories: Biology, Molecular; Biophysics, Medical; Biology, Genetics

Abstract

Quantitative analysis of single molecule experiments show that adding either of two natural polyamines, spermine or spermidine, produced more compact plectonemes in DNA in physiological concentrations of monovalent salt. They also promoted plectoneme formation at lower values of torsion in measurements of extension versus twist. Quantifying changes in the plectonemic DNA using some results from simple rod models suggested that exposure to polyamines reduced the radii and increased the densities of plectonemes. Thus, polyamines may limit the twist density by favoring writhe which maintains the B-form. Although polymerases may significantly stretch the double helix, denature DNA, and produce twist instead of writhe, natural polyamines stabilize base-pairing, limit twist to maintain the B-form, and promote supercoiling, which is conducive to replication and transcription and essential for DNA packaging.