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.
