title: CtrA response regulator binding to the Caulobacter chromosome replication origin is required during nutrient and antibiotic stress as well as during cell cycle progression.
abstract: The Caulobacter crescentus chromosome replication origin (Cori) has five binding sites for CtrA, an OmpR/PhoB family 'response regulator'. CtrA is degraded in replicating 'stalked' cells but is abundant in the non-replicating 'swarmer' cells, where it was proposed to repress replication by binding to Cori. We systematically mutated all Cori CtrA binding sites, and examined their consequences in the contexts of autonomous Cori-plasmid replication and in the natural chromosome locus. Remarkably, the C. crescentus chromosome tolerates severe mutations in all five CtrA binding sites, demonstrating that CtrA is not essential for replication. Further physiological and cell cycle experiments more rigorously supported the original hypothesis that CtrA represses replication. However, our experiments argued against another hypothesis that residual and/or replenished CtrA protein in stalked cells might prevent extra or unscheduled chromosome replication before cell division. Surprisingly, we also demonstrated that Cori CtrA binding sites are very advantageous and can become essential when cells encounter nutrients and antibiotics. Therefore, the CtrA cell cycle regulator co-ordinates replication with viable cell growth in stressful and rapidly changing environments. We argue that this new role for CtrA provided the primary selective pressure for evolving control by CtrA.
authors.affiliation: Department of Microbiology and Immunology, McGill University, 3775 University Street, Montreal, Quebec, Canada.
authors.forename: D Patrick
authors.initials: DP
authors.lastname: Bastedo
authors.forename: Gregory T
authors.initials: GT
authors.lastname: Marczynski
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D016935:Caulobacter crescentus / Q000166:cytology / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D002453:Cell Cycle; D002876:Chromosomes, Bacterial / Q000235:genetics; D004261:DNA Replication; D004269:DNA, Bacterial / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010957:Plasmids; D018741:Replication Origin; D013312:Stress, Physiological; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; C097706:CtrA protein, Caulobacter; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D014157:Transcription Factors