Interaction of the sigma factor and the nusA gene protein of E. coli with RNA polymerase in the initiation-termination cycle of transcription.

The nusA gene protein of E. coli is involved in regulating termination of transcription in vivo. In vitro it causes termination of transcription in the tR2 region of the PR operon of bacteriophage lambda. We have now used a nusA-Sepharose affinity column and gradient sedimentation experiments to show that the nusA protein binds directly, with great specificity, and with equimolar stoichiometry to the E. coli RNA polymerase core enzyme beta beta' alpha 2. The RNA polymerase sigma subunit is able to displace the nusA protein from a beta beta' alpha 2-nusA complex, regenerating RNA polymerase holoenzyme beta beta alpha 2-sigma able selectively to initiate transcription at promoter sites. It is proposed that beta beta' alpha 2-nusA and beta beta' alpha 2-sigma are complementary forms of RNA polymerase that interchange with one another in the initiation-termination cycle of transcription.