| Tectiviridae | |
|---|---|
 | |
| CryoEM model of Enterobacteria phage PRD1 capsid. PDB entry1gw7[1] | |
Virus classification | |
| (unranked): | Virus |
| Realm: | Varidnaviria |
| Kingdom: | Bamfordvirae |
| Phylum: | Preplasmiviricota |
| Class: | Tectiliviricetes |
| Order: | Kalamavirales |
| Family: | Tectiviridae |
| Genera | |
Tectiviridae is a family ofviruses 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 afterchloroform treatment. The name is derived fromLatintectus (meaning 'covered').[4]
Thevirions ofTectiviridae species are non-enveloped, icosahedral and display a pseudo T=25 symmetry.[2] Thecapsid 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 virusgenome. Apical spikes extending about 20 nanometers (nm) protrude from the icosahedrons vertices.[4]
The genome is a single molecule of linear double-strandedDNA 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.[4]
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.[2]
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]