By Marko Hyvönen
Crystallography and Bioinformatics
Department of Biochemistry
University of Cambridge

T7 expression system

The T7 expression system is one of the most powerful ways of producing proteins in Escherichia coli . Developed originally by William Studier in the 1980s it has become the standard of the field. Especially the structural biologists who require large amounts of proteins for their studies are using this system routinely.

The system relies on the fast and specific RNA polymerase of the T7 bacteriophage. The expressed protein is cloned under a strong promoter derived from the T7 phage gene 1 (encoding for the capsid protein of the phage). This promoter is not recognized by the endogenous E.coli RNA polymerase and therefore the cloning of expression constructs can be safely done in a strain lacking the T7 RNA polymerase. For expression of the protein, the vector is transformed into an E.coli strain carrying the T7 RNA polymerase under an inducible lacUV5 promoter. The expression is induced by IPTG.

For more details of the system, follow the links below:

Marko Hyvönen <>
Last modified: Tue Aug 13 15:20:40 BST 2002