Intrinsic viscosity of native and single‐stranded T7 DNA and its relationship to sedimentation coefficient

Abstract

The intrinsic viscosity and sedimentation coefficient of native and single-stranded T7 DNA have been determined at 25⁰C as a function of ionic strength in neutral and alkaline NaCl. The relationship between [η] and S⁰(20,w), is well represented by the Mandelkern-Flory equation over the entire range of conditions between 0.0013 and 1M Na+. An apparent discrepancy between the two methods at moderate to high ionic strengths is probably due to a change in V with ionic strength. It appears that [η] is a more sensitive and reliable measure of molecular expansion for native DNA,but S⁰(20,w) is a better index of conformational change in single strands, since [η] becomes too small to measure conveniently at high ionic strengths. At moderate to high ionic strengths, denaturation leads to a decrease in [η], although unfolded single strands retain considerable viscosity. At sufficiently low ionic strength, the intrinsic viscosity of the single strands becomes higher than that of native DNA, and the effective volume of a single strand approaches that of the native molecule.

Magnetic birefringence study of the electrostatic and intrinsic persistence length of DNA

“…The value obtained from the extrapolation to saturation of the electric orientation (2) is 30% higher (gl - A possible explanation for the comparatively high value found in fibers and films might be related to the difference in the internal field correction: from our definition of Aao, which incorporates the anisotropy of the internal field and which is the measured quantity via Eqs. (7) and (8), it follows that Lao = fallEl1 -aiEL)/Eo with a11 and a 1 being the intrinsic polarizabilities; Eo is the incident electromagnetic field, and Ell and E L the internal field for Eo directed along and perpendicular to the helix axis. It is known from the treatment of hypochromicity as a local field effect30 that in solution, E I < ,311, so that, since la11 > IqI,…”

On the ionic‐strength dependence of the intrinsic viscosity of DNA

“…Equation The electrostatic excluded volume Pel between effective Kuhn segments can be reasonably approximated by4 Pel = 2xL;d (6) Here d is the effective diameter of a Kuhn segment, and it has recently been calculated by Fixman and Skolnick'O: (7) d N K -' (- where [7]0 is the value of the intrinsic viscosity extrapolated to infinite salt concentration, (Lt/Lp)3'2 signifies the hypothetical theta-state expansion: and a,, is a complicated function of a s Weill and des Cloizeaux5 derive a relation for a? which seems to be in better agreement with experiments on uncharged polymers than other theories."…”

Effect of alkali on the size dispersity of mammalian DNA measured by filter elution

“…For example, due to the negative charge of the DNA, changes in the ionic strength of the solvent affect the conformation of the DNA molecule and therefore both its sedimentation coefficient (s) and its intrinsic viscosity (v). As s and 1 vary with ionic strength they remain related over a wide range of ionic strengths as described by the Mandelkern and Flory equation for both native and single-stranded T7 DNA in alkaline or neutral solutions (37). Therefore, the size determinations of mammalian DNA by alkaline sucrose gradients (10,25,26), neutral sucrose gradients (17)(18)(19), and viscoelastometry (20,24) are based on related parameters that can be similarly affected by changes in the hydrodynamic properties of the DNA molecule.…”