Tectivirus

Tectiviridae is a family of viruses with seven species in three 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').

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
Type species
Enterobacteria phage PRD1
Genera

Alpatectivirus
Betatectivirus
Gammatectivirus
Deltatectivirus

Virology

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.

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.

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),[4] P35 (holin),[5] P36 and P37 (homologues of the Rz/Rz1 proteins of phage lambda).[6]

Taxonomy

Tectiviruses have been classified into three major groups: (1) phages that infect Gram-negative bacteria (which lyse the host cell, not forming prophages) (2) those that infect Gram-positive bacteria (forming prophages) and (3) a virus that infects Gluconobacter cerinus. The tectivirus groups have a similar genome size and organization, but they have no detectable sequence similarity at the nucleotide level.[7]

Three genera have been identified in this family: Alphatectivirus - infecting Enterobactericeae; Betatectivirus - infecting Gram positive bacteria; and Gammatectivirus.

Examples[3]

A fourth genus - Deltatectivirus - has been created for a number of phages (Forthebois, WheeHeim and Rhodococcus phage Toil) infecting Actinobacteria hosts.[8]

gollark: I mostly just buy cheap (~£120) phones, which means repair is hard but at least they can be replaced cheaply in two years when they inevitably break.
gollark: Something like that? In any case, it was allegedly vaguely better somehow but made repairs cost more.
gollark: Apple started the trend some years back of fusing the screen glass with the touchscreen digitizer or whatever it is so it's very expensive to replace if it cracks, since you have to replace the entire thing.
gollark: It's possible. They are definitely quite bad to *repair*.
gollark: Ah yes, the "touch bar".

References
  1. San Martín, C; Huiskonen, JT; Bamford, JK; Butcher, SJ; Fuller, SD; Bamford, DH; Burnett, RM (2002). "Minor proteins, mobile arms and membrane-capsid interactions in the bacteriophage PRD1 capsid". Nature Structural Biology. 9 (10): 756–63. doi:10.1038/nsb837. PMID 12219080.
  2. "Viral Zone". ExPASy. Retrieved 15 June 2015.
  3. ICTV. "Virus Taxonomy: 2014 Release". Retrieved 15 June 2015.
  4. Caldentey J, Hänninen AL, Bamford DH (1994). "Gene XV of bacteriophage PRD1 encodes a lytic enzyme with muramidase activity". Eur J Biochem. 225 (1): 341–346. doi:10.1111/j.1432-1033.1994.00341.x. PMID 7925454.
  5. Rydman PS, Bamford DH (2003). "Identification and mutational analysis of bacteriophage PRD1 holin protein P35". J Bacteriol. 185 (13): 3795–3803. doi:10.1128/JB.185.13.3795-3803.2003. PMC 161566. PMID 12813073.
  6. Krupovic M, Cvirkaite-Krupovic V, Bamford DH (2008). "Identification and functional analysis of the Rz/Rz1-like accessory lysis genes in the membrane-containing bacteriophage PRD1". Mol Microbiol. 68 (2): 492–503. doi:10.1111/j.1365-2958.2008.06165.x. PMID 18366440.
  7. Saren, Ari-Matti; Ravantti, Janne J.; Benson, Stacy D.; Burnett, Roger M.; Paulin, Lars; Bamford, Dennis H.; Bamford, Jaana K. H. (15 July 2005). "A Snapshot of Viral Evolution from Genome Analysis of the Tectiviridae Family". Journal of Molecular Biology. 350 (3): 427–440. doi:10.1016/j.jmb.2005.04.059. PMID 15946683.
  8. Caruso SM, deCarvalho TN, Huynh A, Morcos G, Kuo N, Parsa S, Erill I (2019) A novel genus of Actinobacterial Tectiviridae. Viruses 11(12) | doi:10.3390/v11121134. PMID 31817897

Further reading
  • ICTVdB—The Universal Virus Database ICTVdB Management (2006). 00.068. Tectiviridae. In: ICTVdB—The Universal Virus Database, version 3. Büchen-Osmond, C. (Ed), Columbia University, New York, USA
  • Virus Taxonomy: Eighth Report of the International Committee on Taxonomy of Viruses H.V. Van Regenmortel, D.H.L. Bishop, M. H. Van Regenmortel, Claude M. Fauquet (Eds)
  • 68.0.1. Tectivirus
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