title: The Caulobacter crescentus chromosome replication origin evolved two classes of weak DnaA binding sites.
abstract: The Caulobacter crescentus replication initiator DnaA and essential response regulator CtrA compete to control chromosome replication. The C. crescentus replication origin (Cori) contains five strong CtrA binding sites but only two apparent DnaA boxes, termed G-boxes (with a conserved second position G, TGATCCACA). Since clusters of DnaA boxes typify bacterial replication origins, this discrepancy suggested that C. crescentus DnaA recognizes different DNA sequences or compensates with novel DNA-binding proteins. We searched for novel DNA sites by scanning mutagenesis of the most conserved Cori DNA. Autonomous replication assays showed that G-boxes and novel W-boxes (TCCCCA) are essential for replication. Further analyses showed that C. crescentus DnaA binds G-boxes with moderate and W-boxes with very weak affinities significantly below DnaA's capacity for high-affinity Escherichia coli-boxes (TTATCCACA). Cori has five conserved W-boxes. Increasing W-box affinities increases or decreases autonomous replication depending on their strategic positions between the G-boxes. In vitro, CtrA binding displaces DnaA from proximal G-boxes and from distal W-boxes implying CtrA-DnaA competition and DnaA-DnaA cooperation between G-boxes and W-boxes. Similarly, during cell cycle progression, CtrA proteolysis coincides with DnaA binding to Cori. We also observe highly conserved W-boxes in other replication origins lacking E. coli-boxes. Therefore, strategically weak DnaA binding can be a general means of replication control.
authors.affiliation: Dept. Microbiology and Immunology, McGill University, 3775 University Street, Montreal, QC, Canada. james.taylor4@mail.mcgill.ca
authors.forename: James A
authors.initials: JA
authors.lastname: Taylor
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Ouimet
authors.forename: Richard
authors.initials: R
authors.lastname: Wargachuk
authors.forename: Gregory T
authors.initials: GT
authors.lastname: Marczynski
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D016935:Caulobacter crescentus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002876:Chromosomes, Bacterial / Q000235:genetics* / Q000378:metabolism; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D018741:Replication Origin
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C066312:DnaA protein, Bacteria