Figure 18-3: Structure of the T4 virion based on negative stain and cryo-electron microscopy, and crystallographic data. The locations of the protein components are indicated by gene number. The portal vertex composed of gp20 is attached to the upper ring of the neck structure, inside the head itself. The internal tail tube is inside the sheath and itself contains a structural component in its central channel. The baseplate contains short tail fibers made of gp12; these are shown in a stored or folded conformation..