Genus “T5-like Viruses”

Type Species	Enterobacteria phage T5	(T5)

Distinguishing Features

Virions have large heads and have long, kinked tail fibers. The DNA has a single-stranded gap and large terminal repetitions, codes for a type A (E. coli Pol I) DNA polymerase, and is injected in two steps.

Virion Properties

Morphology

Virions have icosahedral heads of about 80  nm in diameter. Tails measure 180 9  nm in Enterobacteria phage T5 (T5) and 160 9  nm in Vibrio phage 149 (type IV), have a subterminal disk with 3 kinked fibers of about 120  nm in length and a conical tip with a single, straight, 50-nm long fiber. Vibrio phage 149 tail fibers have terminal knobs.

Physicochemical and Physical Properties

Virion Mr is 114 10⁶; buoyant density in CsC1 is 1.53  g/cm³; S_20w is 608S.

Nucleic Acid

Genomes are about 121  kbp in size, correspond to 62% of particle weight, and have a G+C content of 44%.

Proteins

Virions contain at least 15 structural proteins (Mr 15.5-125 10³), including 730 copies of the major capsid protein (Mr 44 10³). Type A (E. coli Pol I) DNA polymerase is encoded.

Lipids

Not known.

Carbohydrates

Not known.

Genome Organization and Replication

The genetic map is linear. The genome includes at least 80 genes, is divided into 5 regions, is nonpermuted and has a large terminal repetition of about 10  kbp (8.5% of genome) and 5 major single-stranded gaps at specific sites. It has neither cos nor pac sites. Pre-early, early, and late genes cluster together. Only 8% of DNA is injected immediately after adsorption; the rest follows after 3-4 minutes. Transcription involves modification of host RNA polymerase by phage gene products. DNA replication follows a bidirectional or a rolling-circle mechanism or both. Concatemers are produced.

Biological Properties

Infection is virulent. Phages infect enterobacteria and vibrios.

List of Species Demarcation Criteria in the Genus

Species differ by host range.

List of Species in the Genus

Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names and assigned abbreviations ( ) are:

Species in the Genus

Enterobacteria phage T5	(T5)
Vibrio phage 149 (type IV)	(149)

Tentative Species in the Genus

Enterobacteria phage BF23	(BF23)
Enterobacteria phage PB	(PB)
Enterobacteria phage San 2	(San2)

About 20 additional poorly characterized enterobacterial viruses have been reported that are considered as relatives of T5 morphologically.