The role of Helicobacter pylori DnaA domain I in orisome assembly on a bipartite origin of chromosome replication

The main roles of the DnaA protein are to bind the origin of chromosome replication ( oriC ), to unwind DNA and to provide a hub for the step‐wise assembly of a replisome. DnaA is composed of four domains, with each playing a distinct functional role in the orisome assembly. Out of the four domains, the role of domain I is the least understood and appears to be the most species‐specific. To better characterise Helicobacter pylori DnaA domain I, we have constructed a series of DnaA variants and studied their interactions with H. pylori bipartite oriC . We show that domain I is responsible for the stabilisation and organisation of DnaA‐ oriC complexes and provides cooperativity in DnaA–DNA interactions. Domain I mediates cross‐interactions between oriC subcomplexes, which indicates that domain I is important for long‐distance DnaA interactions and is essential for orisosme assembly on bipartite origins. HobA, which interacts with domain I, increases the DnaA binding to bipartite oriC ; however, it does not stimulate but rather inhibits DNA unwinding. This suggests that HobA helps DnaA to bind oriC , but an unknown factor triggers DNA unwinding. Together, our results indicate that domain I self‐interaction is important for the DnaA assembly on bipartite H. pylori oriC.