Figure 1.

(A) Schematic structure of the P2∼gusA fusion used to study looping repression. In this construct the gal regulatory region contains the external (O_E) and internal (O_I) operator sites, the P2 promoter, and the HU-binding site hbs. The P1 promoter is inactivated by a point mutation. The transcription start site +1 of P1 is used as a reference in the numbering system. (B) Repression of the P2 promoter in vivo. Differential rates of β-glucuronidase synthesis from P2∼gusA in hup⁺ DM0022 (left panel) and in ΔhupAΔhupB strain DM0100 (right panel) cells in the presence of plasmid carrying galR⁺ (filled squares), galR^H327R (open circles), and galR^T322R (open squares).