An improved procedure for the purification of the Escherichia coli RNA polymerase ω subunit

We report an improved procedure for purification of the ω subunit of Escherichia coli RNA polymerase. In contrast to the original procedure, the revised procedure: (i) allows purification of ω entirely from the soluble fraction, obviating the need for denaturation/renaturation, (ii) results in >99% pure ω in only two chromatographic steps, and (iii) improves the yield of purified ω by at least 5-fold. Reconstitution of E. coli RNAP from ω purified by this procedure, as well as purified sigma and core RNAP lacking ω, produces active holoenzyme in vitro, and co-overexpression of ω from a plasmid containing rpoZ and an additional plasmid encoding the other RNAP core subunits results in production of active core enzyme in vivo.