8 nm and have 6 short fibers (Fig. 1).
|
Type Species |
(T7) |
Phage DNA is packaged as unit-size filaments and codes for DNA and RNA polymerases. Phage DNA is nonpermuted and terminally redundant and codes for DNA and RNA polymerases.
Phage heads are icosahedra, measure about 60 nm in diameter, and consist of 72 capsomers (60 hexamers and 12 pentamers; T = 7). Tails measure 17 8 nm and have 6 short fibers (Fig. 1).
Physicochemical and Physical Properties
Virion Mr is about 48 106; buoyant density in CsCl is 1.50 g/cm3; S20w is about 510S. Infectivity is ether and chloroform resistant.
Genomes are about 40 kbp in size (39,936 bp in T7), corresponding to 50% of particle weight, have G+C contents of 50%, and are nonpermuted and terminally redundant. The T7 genome has been fully sequenced.
Particles have at least 9 structural proteins (Mr 13-150 103), including about 460 copies of the major capsid protein (Mr 38 103); 3 proteins are located inside the head. Type B (E. coli Pol II) DNA polymerase and RNA polymerase are encoded. Amino acid sequences are available at GenBank and EMBL.
Not known.
Genome Organization and Replication
The genetic map is linear, nonpermuted and terminally redundant, and comprises about 55 genes, several of which overlap. Related functions cluster together (Fig. 2). Infection results in shut-off of host syntheses and a breakdown of the host genome. The start of replication requires phage-encoded DNA and RNA polymerase and has multiple origins. Transcription proceeds in three waves. Only one strand is transcribed. Replication is bidirectional and produces concatemers by end-to-end joining of intermediate forms. Irregular polyheads are frequently observed. Packaged DNA is cut at fixed sites.
Phages are virulent and are specific for enterics and related Gram-negative bacteria.
List of Species Demarcation Criteria in the Genus
Species differ by host range and insofar as known, DNA homology.
Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, genome sequence accession numbers [ ], and assigned abbreviations ( ) are:
|
Enterobacteria phage T7 |
[V01156] |
(T7) |
|
Enterobacteria phage H |
(H) | |
|
Enterobacteria phage T3 |
(T3) | |
|
Enterobacteria phage W31 |
(W31) | |
|
Enterobacteria phage WPK |
(WPK) | |
|
Enterobacteria phage I |
(I) | |
|
Enterobacteria phage II |
(II) | |
|
Enterobacteria phage ye03 |
(ye03) | |
|
Kluyvera phage Kvp1 |
(Kvp1) | |
|
Pseudomonas phage gh-1 |
(gh-1) |
Tentative Species in the Genus
|
Caulobacter phage Cd1 |
(Cd1) |
|
Enterobacteria phage BA14 |
(Ba14) |
|
Enterobacteria phage 1.2 |
(1.2) |
|
Enterobacteria phage IV |
(IV) |
|
Enterobacteria phage K11 |
(K11) |
|
Enterobacteria phage PTB |
(PTB) |
|
Enterobacteria phage R |
(R) |
|
Enterobacteria phage SP6 |
(SP6) |
|
Enterobacteria phage Y |
(Y) |
|
Enterobacterial phage ViIII |
(ViIII) |
|
Pseudomonas phage PLS27 |
(PLS27) |
|
Pseudomonas phage PLS743 |
(PLS743) |
|
Pseudomonas phage Pssy9220 |
(Psy9220) |
|
Rhizobium phage 2 |
(2) |
|
Rhizobium phage S |
(S) |
|
Vibrio phage III |
(III) |
|
|  |