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Summary

Replication of the bacterial chromosome is initiated by the binding of the DnaA protein to a unique DNA region, called oriC. Many regulatory factors in numerous species act by controlling the ability of DnaA to bind and unwind DNA, but the Helicobacter pylori genome does not contain homologues to any of these factors. Here, we describe HobA, a novel protein essential for initiation of H. pylori chromosome replication, which is conserved among, and unique to, epsilon proteobacteria. We demonstrate that HobA interacts specifically via DnaA with the oriC–DnaA complex. We postulate that HobA is essential for correct formation and stabilization of the orisome by facilitating the spatial positioning of DnaA at oriC. Consistent with its function, overexpression of hobA had no effect on growth of H. pylori, whereas depletion of HobA led to growth arrest and failure to initiate replication. In conclusion, HobA may be the first identified of a new group of initiation factors common to epsilon proteobacteria.