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. 2019 Sep 12;15(9):e1008320. doi: 10.1371/journal.pgen.1008320

Fig 2. Origin organization and recognition in bacteria.

Fig 2

A) Schematic of the architecture of E. coli origin oriC, Thermotoga maritima oriC, and the bipartite origin in Helicobacter pylori. The DUE is flanked on one side by several high- and weak-affinity DnaA-boxes as indicated for E. coli oriC. B) Domain organization of the E. coli initiator DnaA. The magenta circle indicates the single-strand DNA binding site. C) Models for origin recognition and melting by DnaA. In the two-state model (left panel), the DnaA protomers transition from a dsDNA binding mode (mediated by the HTH-domains recognizing DnaA-boxes) to an ssDNA binding mode (mediated by the AAA+ domains). In the loop-back model, the DNA is sharply bent backwards onto the DnaA filament (facilitated by the regulatory protein IHF [40]) so that a single protomer binds both duplex and single-stranded regions. In either instance, the DnaA filament melts the DNA duplex and stabilizes the initiation bubble prior to loading of the replicative helicase (DnaB in E. coli). HTH–helix-turn-helix domain, DUE–DNA unwinding element, IHF–integration host factor.