Figure 1.

(A) In the Arc-operator complex (2), the N-terminal arms and β-sheet of each Arc dimer are positioned to contact the operator DNA, and the side chains of Phe-10 and Phe-10′ interact with phosphate oxygen and ribose atoms of the DNA backbone. These contacts between Phe-10 and the DNA backbone contribute to both the specificity and affinity of operator binding as described in the text. This panel and Fig. 3A were prepared by using molscript (26). (B) Superimposition of the conformation of the Phe-10 side chain in unbound Arc (blue) and operator-bound Arc (yellow).