Tectivirus

Tectiviridae is a family of viruses with 12 species in five genera. Bacteria serve as natural hosts.^[2][3] Tectiviruses have no head-tail structure, but are capable of producing tail-like tubes of ~ 60×10 nm upon adsorption or after chloroform treatment. The name is derived from Latin tectus (meaning 'covered').^[4]

Tectiviridae
CryoEM model of Enterobacteria phage PRD1 capsid. PDB entry 1gw7[1]
Virus classification
(unranked):	Virus
Realm:	Varidnaviria
Kingdom:	Bamfordvirae
Phylum:	Preplasmiviricota
Class:	Tectiliviricetes
Order:	Kalamavirales
Family:	Tectiviridae
Genera
See text

Virology

Entry mechanism Enterobacteria phage PRD1

The virions of Tectiviridae species are non-enveloped, icosahedral and display a pseudo T=25 symmetry.^[2] The capsid has two layers. The outer layer is a protein structure of 240 capsid proteins trimers, and the inner one is a proteinaceous lipid membrane which envelopes the virus genome. Apical spikes extending about 20 nanometers (nm) protrude from the icosahedrons vertices.^{[citation needed]}

The genome is a single molecule of linear double-stranded DNA of 15 kilobases in length, and has 30 open reading frames.^[2] It forms a tightly packed coil and encodes several structural proteins. It encodes about 30 proteins that are transcribed in operons. At least 9 structural proteins are present in the viron. The genome is about 66 megadaltons in weight and constitutes 14–15% of the virion by weight. Lipids constitute a further 15% by weight. Carbohydrates are not present.^{[citation needed]}

Life cycle

Viral replication is cytoplasmic. Entry into the host cell is achieved by adsorption into the host cell.^[2] After adsorption to the host cell surface the virion extrudes a tail-tube structure through a vertex for genome delivery into the host. Replication follows the DNA strand displacement model. DNA-templated transcription is the method of transcription.^[2] Capsid proteins polymerize around a lipoprotein vesicle translocated in the cytoplasm by virion assembly factors.

Mature virons are released by lysis, which, in the case of PRD1, is achieved with the aid of virus-encoded lysis machinery consisting of four proteins: P15 (endolysin),^[5] P35 (holin),^[6] P36 and P37 (homologues of the Rz/Rz1 proteins of phage lambda).^[7]

Taxonomy

Tectiviridae contains the following genera and species:^[3]

• Alphatectivirus
  • Alphatectivirus PR4
  • Alphatectivirus PRD1
• Betatectivirus
  • Betatectivirus AP50
  • Betatectivirus Bam35
  • Betatectivirus GIL16
  • Betatectivirus sato
  • Betatectivirus sole
  • Betatectivirus Wip1
• Deltatectivirus
  • Deltatectivirus forthebois
  • Deltatectivirus wheeheim
• Epsilontectivirus
  • Epsilontectivirus toil
• Gammatectivirus
  • Gammatectivirus GC1

Other unassigned phages:^[8]

• Thermus virus phiKo
• Microbacterium virus Badulia
• Microbacterium virus MuffinTheCat