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DNA toroids, bundles, fibers and spherulites inside and outside of the virus capsid
In double stranded DNA bacteriophages, a single semi-rigid DNA chain with a 50-nm persistence length is confined in a volume of comparable dimension, which imposes high geometrical constraints. This confinement raises the question of the possible organization of the chain inside the capsid, a key element to understanding how the genome can be transferred efficiently to the bacteria during the infection process. Using cryo-electron microscopy, we focus on the organization of the genome. We show how the chain undergoes a series of phase transitions upon progressive ejection when the encapsidated DNA length decreases. Each chain being isolated from the others inside its own capsid, we can also analyse the collapse of each individual molecule into toroidal and more complex structures.
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