Identification of a putative chromosomal replication origin from Helicobacter pylori and its interaction with the initiator protein DnaA

The key elements of the initiation of Helicobacter pylori chromosome replic ation, DnaA protein and putative oriC region, have been characterized. The gene arrangement in the H.pylori dnaA region differs from that found in man y other eubacterial dnaA regions (rnpA-rmpK-dnaA-dnaN-recF-gyrB). Helicobac ter pylori dnaA is flanked by two open reading frames with unknown function , while dnaN-gyrB and rnpA-rmpH loci are separated from the dnaA gene by 60 0 and 90 kb, respectively. We show that the dnaA gene encoding initiator pr otein DnaA is expressed in H.pylori cells. The H.pylori DnaA protein, like other DnaA proteins, can be divided into four domains. Here we demonstrate that the C-terminal domain of H.pylori DnaA protein is responsible for DNA binding. Using in silico and in vitro studies, the putative oriC region con taining five DnaA boxes has been located upstream of the dnaA gene. DNase I and gel retardation analyses show that the C-terminal domain of H,pylori D naA protein specifically binds each of five DnaA boxes.