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A Kinetic Analysis of DNA Ejection from Tailed Phages Revealing the Prerequisite Activation Energy

Eric Raspaud ^*, Thomas Forth ^*, Carlos São-José , Paulo Tavares  and Marta de Frutos ^*

^* Laboratoire de Physique des Solides, Université Paris-Sud, CNRS, UMR 8502, F-91405 Orsay cedex, France; Instituto de Ciência Aplicada e Tecnologia e Departamento de Biologia Vegetal, Facultade de Ciências de Lisboa, Ed. ICAT, 1749-016 Lisboa, Portugal; and Unité de Virologie Moléculaire et Structurale, UMR CNRS 2472, UMR INRA 1157, and IFR 115, 91198 Gif-sur-Yvette, France

Correspondence: Address reprint requests to Marta de Frutos, E-mail: defrutos{at}lps.u-psud.fr.

All tailed bacteriophages follow the same general scheme of infection: they bind to their specific host receptor and then transfer their genome into the bacterium. DNA translocation is thought to be initiated by the strong pressure due to DNA packing inside the capsid. However, the exact mechanism by which each phage controls its DNA ejection remains unknown. Using light scattering, we analyzed the kinetics of in vitro DNA release from phages SPP1 and (Siphoviridae family) and found a simple exponential decay. The ejection characteristic time was studied as a function of the temperature and found to follow an Arrhenius law, allowing us to determine the activation energy that governs DNA ejection. A value of 25–30 kcal/mol is obtained for SPP1 and , comparable to the one measured in vitro for T5 (Siphoviridae) and in vivo for T7 (Podoviridae). This suggests similar mechanisms of DNA ejection control. In all tailed phages, the opening of the connector-tail channel is needed for DNA release and could constitute the limiting step. The common value of the activation energy likely reflects the existence for all phages of an optimum value, ensuring a compromise between efficient DNA delivery and high stability of the virus.

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