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In viro DNA condensation in the extended Ubbink-Odijk model

The shape of condensed DNA toroids is in the Ubbink-Odijk (UO) model [1] determined by the interplay of elastic energy of wound DNA and the surface energy of the DNA strands exposed on the toroid surface. The hugely complicated microscopic situation with myriad of molecular interactions is thus reduced to a continuum model containing only two parameters: the DNA persistence length and the »surface tension« of the DNA. The UO model predicts DNA toroid shapes which depend on a single, combined parameter mixing the elastic and surface energy contributions of the free energy. I will show how the UO model can be extended to study the formation of a condensed DNA toroid within a bacteriophage capsid. This involves adding a third (second) parameter to the model which signifies the effective DNA-capsid interaction. The predictions of the extended model are shown to compare favorably with experimental data [2]. The effective DNAcapsid interaction is found to depend on the condensation agent (PEG vs spermine). [1] J. Ubbink and T. Odijk, Deformation of toroidal DNA condensates under surface stress, Europhys. Lett. 33 (1996). [2] Amélie Leforestier, Antonio Šiber, Françoise Livolant and Rudolf Podgornik, Biophys. J. 100, 2209 (2011).

DNA; torus; surface; adhesion; virus; elasticity

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