Cloning and expression of the gene for bacteriophage T7 RNA polymerase.

Abstract

The complete coding sequence of the gene for bacteriophage T7 RNA polymerase (T7 gene 1) was cloned in the plasmid pBR322. Large amounts of active enzyme can be accumulated in Escherichia coli when the cloned gene is transcribed from the lac UV5 promotor. A protease activity that apparently can nick the protein without causing it to fall apart can be a problem during purification, but a procedure is described that gives good yields of essentially homogeneous, highly active enzyme suitable for biochemical and physical studies. T7 RNA polymerase has a stringent specificity for its own promoters and will selectively transcribe DNA that was linked to such a promoter. This specificity makes the enzyme useful both for producing specific RNA in vitro and for directing the expression of selected genes inside the cell. Having the cloned gene also makes possible a detailed mutational analysis of the functioning of T7 RNA polymerase.