Expression and purification of active recombinant T7 RNA polymerase from E. coli

For large-scale transcription reactions or for cost savings, a laboratory may want to prepare its own recombinant T7-, SP6-, or T3-phage RNA polymerases. It is convenient to perform this preparation every 2-3 years and have a consistent and reliable source of phage RNA polymerase for many in vitro transcription reactions. In the protocol presented here, the recombinant plasmid expressing T7 RNA polymerase (RNAP) as a his6-tagged molecule is under an isopropyl β-d-1-thio-galactopyranoside (IPTG)-inducible promoter. The bacteria are lysed by sonication, the his6-tagged protein in the bacterial lysate is purified by binding to Ni-NTA agarose, and the resin is then extensively washed and eluted with imidazole. The purified enzyme is dialyzed against a glycerol-containing storage buffer and can then be stored for months or years at -20°C.