FIG. 3.

Interactions between CRP and RNAP at a class I and a class II promoter. When bound at a class I promoter, CRP uses AR1 (small black semicircle) in the promoter-proximal subunit to contact the α-CTD. When bound at a class II promoter, wild-type CRP makes two contacts with RNAP by using AR1 in the promoter-distal subunit to contact the α-CTD and AR2 (small black rectangle) in the promoter-proximal subunit to contact the α-NTD. The CRP^K52N mutant possesses a third activating region, designated AR3 (small black triangle), that has been proposed to contact the ς subunit (see text).