Myoviridae. Myoviridae

Description of Myoviridae adapted from ICTVdb Virion Properties Morphology Phages consist of a head and a tail and are not enveloped. Head separated from tail by a neck, tail complex, consisting of a central tube and a contractile sheath, provided with a collar, base plate, 6 short spikes and 6 long fibbers. Contraction seems to require ATP. Phage has a a tail with helical and a head with icosahedral symmetry or symmetry which is derived from a basic icosahedral structure by adding rows of capsomers to the capsid (T=13). The head is isometric to prolate in shape and has a diameter of 50-110 nm. Capsids appear hexagonal in outline. The capsid consists of 152 capsomers. The tail is a rigid, long and thick, contractile tube which is cross-banded, or is obliquely striated with a crisscrossed appearance with a length of (80-)95-111(-455) nm and a width of 16-20 nm. Axial canal is distinct. Basic helix is obvious. Tail has a collar, a base plate, spikes, fibers, and a sheath, which is separated from the head by a neck; sheath is composed of stacked rings. During contraction, sheath subunits of contractile tails slide over each other and the sheath becomes shorter and thicker, sheath is 10-15 nm long when contracted. Tail has 6 long terminal fibers, 6 short spikes and a small base plate. The central core of phage tail is helical. Physicochemical and Physical Properties Virions have a buoyant density in CsCl of 1.41-1.51 g cm-3. Nucleic Acid The Mr of the genome constitutes 48% of the virion by weight. The genome is not segmented and contains a single molecule of linear double-stranded DNA. The complete genome is 33600-170000 nucleotides long. Genome is sequenced, but only an estimate is available, complete sequence is 33600-170000 nucleotides long. The genome has a guanine + cytosine content of 35 %. The genome contains unusual bases, they are 5-hydroxy-methyl cytosine (instead of thymidine). Double stranded DNA is circularly permuted. The genome has terminally redundant sequences. Proteins The viral genome encodes structural proteins and non-structural proteins. Lipids Lipids are not reported.