Eur. Phys. J. E (2008) 26: 317-325
https://doi.org/10.1140/epje/i2008-10330-7

Regular Article

Packing nanomechanics of viral genomes

¹ Institute of Physics, P.O. Box 304, 10001, Zagreb, Croatia
² Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, SI-1000, Ljubljana, Slovenia
³ Department of Theoretical Physics, J. Stefan Institute, SI-1000, Ljubljana, Slovenia
⁴ Laboratory of Physical and Structural Biology, National Institutes of Health, MD 20892-0924, Bethesda, USA

^* e-mail: rudolf.podgornik@fmf.uni-lj.si

Received: 28 March 2008
Accepted: 7 May 2008
Published online: 5 June 2008

Abstract

We investigate the osmotic equilibrium between a bulk polyethylene glycol (PEG) solution and DNA tightly packed in a spherical capsid. We base our analysis on the equations of thermodynamic equilibrium in terms of osmotic pressure. The equality between external osmotic pressure of PEG and osmotic pressure of tightly packed DNA gives us the DNA encapsidation curves. In this way we directly connect the wealth of existing osmotic pressure data for DNA in the bulk with the DNA encapsidation curves within small viral capsids. Specific calculations are made for a monovalent salt, Na⁺ -DNA and a divalent salt, Mn²⁺ -DNA that have quite different DNA encapsidation behaviors. The main conclusion of our work is that bending energy of DNA is of minor importance regarding the encapsidated DNA length, but has a non-negligible influence on the density distribution of DNA within the capsid.