T7 DNA polymerase
The T7 DNA polymerase of the T7 bacteriophage is a DNA-dependent DNA polymerase responsible for the fast rate of T7 phage DNA replication in vivo. The polymerase consists of a 1:1 complex of the viral T7 gene 5 protein (80kDA) and the E. coli thioredoxin (12kDA).
It lacks a 5' -> 3' exonuclease domain, but the 3' -> 5' exonuclease activities are approximately 1000-fold greater than that of Klenow fragment. The exonuclease activity appears to be responsible for the high fidelity of this enzyme and prevents strand displacement synthesis 
This polymerase is unique due to its considerable processivity, or ability to stay on DNA for a greater than average number of base pairs. It is also suitable for site-directed mutagenesis  but is not recommended for DNA sequencing applications.
- Sambrook, J., Russell, D.W. (2001). "Molecular Cloning: A Laboratory Manual, Third edition". Cold Spring Harbor Laboratory Press (Cold Spring Harbor, New York, 2001.).
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- BEBENEK, K. et al. (1989). "The use of native T7 DNA polymerase for site-directed mutagenesis.". Nucl. Acids Res. 17 (13): 5408. doi:10.1093/nar/17.13.5408. PMC 318147. PMID 2668888.
- Doublie S., Tabor S., Long A., Richardson C., and Ellenberger T. (1998). "Crystal Structure of a Bacteriophage T7 DNA Replication complex at 2.2 A Resolution.". Nature 391 (6664): 251–258. doi:10.1038/34593. PMID 9440688.
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