DNA poised for release in bacteriophage φ29

We present here the first asymmetric, three-dimensional reconstruction of a tailed dsDNA virus, the mature bacteriophage phi 29, at subnanometer resolution. This structure reveals the rich detail of the asymmetric interactions and conformational dynamics of the phi 29 protein and DNA components, and provides novel insight into the mechanics of virus assembly' For example, the dodecameric head-tail connector protein undergoes significant rearrangement upon assembly into the virion. Specific interactions occur between the tightly packed dsDNA and the proteins of the head and tail. Of particular interest and novelty, an similar to 60 angstrom diameter toroid of dsDNA was observed in the connector-lower collar cavity. The extreme deformation that occurs over a small stretch of DNA is likely a consequence of the high pressure of the packaged genome. This toroid structure may help retain the DNA inside the capsid prior to its injection into the bacterial host.