The interaction domains of the DnaA and DnaB replication proteins of Escherichia coli

The initiation of chromosome replication in Escherichia coil requires the r ecruitment of the replicative helicase DnaB from the DnaBC complex to the u nwound region within the replication origin oriC, supported by the oriC-bou nd initiator protein DnaA. We defined physical contacts between DnaA and Dn aB that involve residues 24-86 and 130-148 of DnaA and residues 154-210 and 1-156 of DnaB respectively. We propose that contacts between DnaA and DnaB occur via two interaction sites on each of the proteins. interaction domai n 24-86 of DnaA overlaps with its N-terminal homo-oligomerization domain (r esidues 1-86). Interaction domain 154-210 of DnaB overlaps or is contiguous with the domains known to interact with plasmid initiator proteins. Loadin g of the DnaBC helicase in vivo can only he performed by DnaA derivatives c ontaining (in addition to residues 24-86 and the DNA-binding domain 4) a st ructurally intact domain 3. Nucleotide binding by domain 3 is, however, not required. The parts of DnaA required for replication of pSC101 were clearl y different from those used for helicase loading. Domains 1 and 4 of DnaA, but not domain 3, were found to be involved in the maintenance of plasmid p SC101.