MEMBRANE-MEDIATED RELEASE OF NUCLEOTIDE FROM ALL INITIATOR OF CHROMOSOMAL REPLICATION, ESCHERICHIA-COLI DNAA, OCCURS WITH INSERTION OF A DISTINCT REGION OF THE PROTEIN INTO THE LIPID BILAYER

DnaA protein, the initiator protein of E. coli chromosomal replication , can be rejuvenated from an inactive ADP form to active ATP-DnaA prot ein by acidic phospholipids in a fluid bilayer. Cross-linking studies with the photoactivable phospholipid analog oxy]carbonyl]nonanoyl]-sn- glycero-3-phosphocholine reveal insertion of DnaA protein into the hyd rophobic region of the bilayer; this insertion is accompanied by membr ane-mediated dissociation of the tightly bound allosteric nucleotides ADP and ATP. Photolabeling of DnaA protein occurred with membrane prop erties that resembled those needed for reactivation of ADP-DnaA protei n; efficient labeling of DnaA protein was observed only when the lipid analog was incorporated into anionic vesicles and the temperature dur ing treatment was above the gel to Liquid crystalline phase transition . Predominant hydrophobic photolabeling was localized within a single region of DnaA protein, a region that contains putative amphipathic he lices and has been shown to contain information essential for function al interaction with membranes.