The σ70 substitutions 551-552,554-555A (A) eliminate
the interaction of the β-flap with σ70
region 4 whereas substitutions 584-588A (B) do not impair the interaction of
σ70 region 4 with the β-flap.
Cultures contained a pBRα-σ70 plasmid, which
had σ70 region 4 (σ70 4) with
the indicated substitutions, and either the control plasmid,
pACλcI32, the pcI plasmid that lacks a fused bait protein, or
the pcI-β-flap plasmid (β-flap). Graphs show
β-galactosidase activity (in Miller units) versus the
concentration of IPTG present in the cultures.