Experimental comparison of forces resisting viral DNA packaging and driving DNA ejection

Nicholas Keller, Zachary T. Berndsen, Paul J. Jardine, and Douglas E. Smith
Phys. Rev. E 95, 052408 – Published 17 May 2017

Abstract

We compare forces resisting DNA packaging and forces driving DNA ejection in bacteriophage phi29 with theoretical predictions. Ejection of DNA from prohead-motor complexes is triggered by heating complexes after in vitro packaging and force is inferred from the suppression of ejection by applied osmotic pressure. Ejection force from 0% to 80% filling is found to be in quantitative agreement with predictions of a continuum mechanics model that assumes a repulsive DNA-DNA interaction potential based on DNA condensation studies and predicts an inverse-spool conformation. Force resisting DNA packaging from 80% to 100% filling inferred from optical tweezers studies is also consistent with the predictions of this model. The striking agreement with these two different measurements suggests that the overall energetics of DNA packaging is well described by the model. However, since electron microscopy studies of phi29 do not reveal a spool conformation, our findings suggest that the spool model overestimates the role of bending rigidity and underestimates the role of intrastrand repulsion. Below 80% filling the inferred forces resisting packaging are unexpectedly lower than the inferred ejection forces, suggesting that in this filling range the forces are less accurately determined or strongly temperature dependent.

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  • Received 11 February 2017

DOI:https://doi.org/10.1103/PhysRevE.95.052408

©2017 American Physical Society

Physics Subject Headings (PhySH)

Physics of Living Systems

Authors & Affiliations

Nicholas Keller1, Zachary T. Berndsen1,2, Paul J. Jardine3, and Douglas E. Smith1,*

  • 1Department of Physics, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA
  • 2Department of Chemistry and Biochemistry, University of California, San Diego, California 92093, USA
  • 3Department of Diagnostic and Biological Sciences and Institute for Molecular Virology, University of Minnesota, 515 Delaware Street SE, Minneapolis, Minnesota 55455, USA

  • *des@ucsd.edu

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Vol. 95, Iss. 5 — May 2017

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