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

See text

Tectiviridae is a family of viruses with 10 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]


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[edit]

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]


Tectiviridae contains the following genera and species:[3]

Other unassigned phages:[8]


  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. S2CID 32856328.
  2. ^ a b c d e "Viral Zone". ExPASy. Retrieved 15 June 2015.
  3. ^ a b "Virus Taxonomy: 2020 Release". International Committee on Taxonomy of Viruses (ICTV). March 2021. Retrieved 22 May 2021.
  4. ^ "ICTV Ninth Report; 2009 Taxonomy Release: Tectiviridae". ICTV. Archived from the original on 24 April 2019. Retrieved 18 September 2020.
  5. ^ 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.
  6. ^ 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.
  7. ^ 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.
  8. ^ Unclassified Tectiviridae. NCBI Taxonomy.

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