Figure 10.

One of the six helical strands of gp18 that form the T4 tail sheath in the extended (green) and contracted (brown) states. The hexagonally shaped baseplate, tail tube and collar of the extended tail are also shown (blue). The extended sheath makes about one turn around the tail tube, whereas the contracted sheath makes about two turns, thus causing the tail tube and head to rotate while entering the periplasmic space of the E. coli host. (Adapted from Kostyuchenko et al., 2005 ▶.)