Assembly and infection process of bacteriophage T4.

Bacterophage T4 consists of three parts, namely, a head, a tail, and six tail fibers, each of which is assembled along an independent pathway and then joined. In contrast to simple plant viruses such as tobacco mosaic virus, disassembly and reassembly of the virion is not possible. This is due mainly to the fact that the assembly involves not only irreversible steps such as cleavage of covalent bonds of some constituent proteins, but also that it requires a scaffold and involves the inner membrane of the host cell. Another unique feature of the assembly as a biological nanomachine is the involvement of specific protein devices such as a "ruler molecule," which determines the length of the tail, an ATP-driven DNA packaging protein complex, and phage-encoded molecular chaperones. Recent structural biological studies of the phage started to unveil the molecular mechanics of structural transformation of the tail upon infection.