Fig. 4.

Complete dynamic model of the T4 injection machinery interacting with the host cell predicts the internal energy of the contractile sheath that drives the injection process. (A) The sheath begins in the (high-energy) extended state where the tip of the tail tube remains 100 Å from the cell membrane. (B) The sheath contracts about 100 Å so that the tip of the tail tube touches the outer cell membrane. (C) Further contraction of the sheath produces, in sequence, cell indentation, rupture of the outer cell membrane (after 60-Å indentation), and penetration into the (viscous) periplasmic space. (D) The fully contracted sheath with zero elastic energy. Note that in this simulation, ${\eta }_w=30\hspace{0.17em}\hspace{0.17em}\text{Pa}\cdot \text{s}$ and ${\overline{\eta }}_{int}=0.005\hspace{0.17em}\hspace{0.17em}\text{Pa}\cdot \text{s}.$