Theoretical evidence for the coupling of winding to compression in the solution conformation of duplex DNA

✍ Scribed by Gerald S. Manning

• Publisher: Wiley (John Wiley & Sons)
• Year: 1981
• Tongue: English
• Weight: 862 KB
• Volume: 20
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1981.360201105

✦ Synopsis

Abstract

Published data indicate linear variation of the duplex winding of DNA with logarithm of the ionic strength. We show that this observation is a natural prediction of a current poly‐electrolyte theory if structural coupling between duplex rotation angle (rotation per base pair) and step height (axial translation per base pair) is assumed. We show also that the coupling must then be negative: the positive winding on augmentation of the ionic strength must be accompanied by a decrement of step height, or axial compression. Cation species specificity of winding, CD spectra, and cation binding affinity are discussed in terms of local variation of dielectric shielding, using current accurate data for dielectric constants of aqueous salt solutions. One need not invoke specific complexation of cations, for which there is no present evidence (in aqueous solution), to explain any of these effects. The analysis is limited to low and moderate ionic strengths. Experimental observations at very high ionic strengths are puzzling and possibly conflicting. It is concluded that a need exists for systematic extension of available duplex winding data throughout the region of moderate to very high ionic strengths. It would be useful to extend the region at the low end as well, in order to distinguish clearly the behavior predicted by our model from that predicted by a referee on the basis of an alternate model described herein.