title: A multifunctional plasmid-encoded replication initiation protein both recruits and positions an active helicase at the replication origin.
abstract: The DnaA replication initiation protein has been shown to be essential for DNA strand opening at the AT-rich region of the replication origin of the Escherichia coli chromosome as well as serving to recruit and position the DnaB replicative helicase at this open region. Homologues of the dnaA gene of E. coli have been found in most bacterial species, and the DnaA protein has been shown to be required for the initiation of replication of both chromosomal and plasmid DNA. For several plasmid elements it has been found that a plasmid-encoded initiation protein is required along with the DnaA protein to bring about opening of the AT-rich region at the replication origin. The broad host range plasmid RK2 encodes two forms of its replication initiation protein (TrfA-33 and TrfA-44) that differ by an additional 98 aa at the N terminus of the larger (TrfA-44) form. Both forms initiate replication of RK2 in E. coli in vitro by a DnaA-dependent mechanism. However, as shown in this study, TrfA-44 specifically interacts with the DnaB replicative helicase of Pseudomonas putida and Pseudomonas aeruginosa and initiates the formation of a prepriming open complex in the absence of DnaA protein. Thus, the TrfA-44 initiation protein has the multifunctional properties of recruiting and positioning an active form of the DnaB helicase at the RK2 replication origin by a DnaA-independent process. This unique property for a replication initiation protein undoubtedly plays an important role in extending the host range of the RK2 antibiotic resistance plasmid.
authors.affiliation: Division of Biological Sciences and Center for Molecular Genetics, University of California at San Diego, La Jolla, CA 92093-0322, USA.
authors.forename: Yong
authors.initials: Y
authors.lastname: Jiang
authors.forename: Marcin
authors.initials: M
authors.lastname: Pacek
authors.forename: Donald R
authors.initials: DR
authors.lastname: Helinski
authors.forename: Igor
authors.initials: I
authors.lastname: Konieczny
authors.forename: Aresa
authors.initials: A
authors.lastname: Toukdarian
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D004265:DNA Helicases / Q000378:metabolism*; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D053488:DnaB Helicases; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000378:metabolism; D016958:Pseudomonas putida / Q000235:genetics / Q000378:metabolism; D018741:Replication Origin
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C066312:DnaA protein, Bacteria; D029968:Escherichia coli Proteins; C067405:TrfA protein, E coli; D004265:DNA Helicases; D053488:DnaB Helicases