Figure 7. Model for gp67 Function.

(A) At most –10/–35 promoters, which are not dependent on αCTD/UP-element interactions, gp67 joins the Sau RNAP holoenzyme through its interaction with σ^A₄. However, gp67 does not block any of the functions of σ^A₄ and does not inhibit RNAP.

(B) At promoters where activity depends on αCTD/UP-element interactions, gp67 joins the RNAP holoenzyme through its interaction with σ^A₄ and inhibits transcription initiation by preventing αCTD binding to the promoter-proximal UP-element subsite, or to both proximal and distal subsites (shown).