Building the bacterial orisome: high-affinity DnaA recognition plays a role in setting the conformation of oriC DNA.

During assembly of the E. coli pre-replicative complex (pre-RC), initiator DnaA oligomers are nucleated from three widely separated high-affinity DnaA recognition sites in oriC. Oligomer assembly is then guided by low-affinity DnaA recognition sites, but is also regulated by a switch-like conformational change in oriC mediated by sequential binding of two DNA bending proteins, Fis and IHF, serving as inhibitor and activator respectively.