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T7 phage: Wikis


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Bacteriophage T7 is a phage 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).

The virus is said to have 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.

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.[1] 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.


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. In other words, clone a gene and you get expression. Clone with a T7 promoter and you turbo charge it.


  1. ^ Chan, Leon Y.; Kosuri, Sriram; Endy, Drew (2005). "Refactoring bacteriophage T7". Molecular Systems Biology 1 (1): 2005.0018. doi:10.1038/msb4100025.  

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