Fig 6.

DNA path through the connector, lower collar, and tail tube viewed in segmented representations of the ϕ29 virion density map (~2σ threshold). (A) A cylindrical column of high density emerges from the bulk DNA (red) in the head, slightly above the connector (yellow), and follows a path along the connector-tail axis into the gp10/11 cavity where it transforms into a toroid-shaped structure. From there, a column of high density emerges at the bottom of the toroid, continues for ~80 Å along the tail tube axis, after which weaker density (white) fills the rest of the tube, ending at the gp9 tail knob cavity (not shown). Four arrows identify regions in the plane of the cross section where the DNA and gp10 (yellow) and gp11 (green) are in close contact. These contacts, along with the apparent tight interactions between the DNA-gp3 and the end of the tail tube, might collectively help prime the highly pressurized DNA for release upon attachment of the phage to the host. (B) Tilted, close-up view of the DNA toroid and its surroundings. Color scheme matches that used in Figure 1.