| Enterobacteria phage T7 | |
|---|---|
| Virus classification | |
| Group: | Group I (dsDNA) |
| Order: | Caudovirales |
| Family: | Podoviridae |
| Genus: | T7-like viruses |
| Species: | T7 phage |
Bacteriophage T7 is a bacteriophage capable of infecting susceptible bacterial cells. It infects most strains of Escherichia coli (including E. coli O157:H7, a strain of E. coli which can cause foodborne illness).
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The virus has complex structural symmetry, with a capsid of the phage that is spherical with an inner diameter of 55 nm and a tail 19 nm in diameter and 28.5 nm long attached to the capsid. The head of the phage particle contains the roughly 40 kbp dsDNA genome of T7. [1]
Gp5 (encoded by gene gp5) is T7 phage's DNA polymerase. T7 polymerase uses E. coli's endogenous thioredoxin as a sliding clamp during phage DNA replication (though thioredoxin normally has a different function). The sliding clamp functions to hold the polymerase onto the DNA, which increases the rate of synthesis; initiation, the process by which a polymerase binds to DNA, is time-consuming.
The T7 promoter sequence is used extensively in molecular biology due to its extremely high affinity for RNA polymerase and thus high level of expression.
T7 has been used as a model in synthetic biology. Chan et al. (2005) "refactored" the genome of T7, replacing approximately 12 kbp of its genome with engineered DNA.[2] The engineered DNA was designed to be easier to work with in a number of ways: individual functional elements were separated by restriction endonuclease sites for simple modification, and overlapping protein coding domains were separated and, where necessary, modified by single base pair silent mutations.