title: Accelerated growth in the absence of DNA replication origins.
abstract: DNA replication initiates at defined sites called origins, which serve as binding sites for initiator proteins that recruit the replicative machinery. Origins differ in number and structure across the three domains of life and their properties determine the dynamics of chromosome replication. Bacteria and some archaea replicate from single origins, whereas most archaea and all eukaryotes replicate using multiple origins. Initiation mechanisms that rely on homologous recombination operate in some viruses. Here we show that such mechanisms also operate in archaea. We use deep sequencing to study replication in Haloferax volcanii and identify four chromosomal origins of differing activity. Deletion of individual origins results in perturbed replication dynamics and reduced growth. However, a strain lacking all origins has no apparent defects and grows significantly faster than wild type. Origin-less cells initiate replication at dispersed sites rather than at discrete origins and have an absolute requirement for the recombinase RadA, unlike strains lacking individual origins. Our results demonstrate that homologous recombination alone can efficiently initiate the replication of an entire cellular genome. This raises the question of what purpose replication origins serve and why they have evolved.
authors.affiliation: School of Biology, University of Nottingham, Queen's Medical Centre, Nottingham, NG7 2UH, UK.
authors.forename: Michelle
authors.initials: M
authors.lastname: Hawkins
authors.affiliation: DeepSeq, University of Nottingham, Queen's Medical Centre, Nottingham, NG7 2UH, UK.
authors.forename: Sunir
authors.initials: S
authors.lastname: Malla
authors.affiliation: DeepSeq, University of Nottingham, Queen's Medical Centre, Nottingham, NG7 2UH, UK.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Blythe
authors.affiliation: School of Biology, University of Nottingham, Queen's Medical Centre, Nottingham, NG7 2UH, UK.
authors.forename: Conrad A
authors.initials: CA
authors.lastname: Nieduszynski
authors.affiliation: School of Biology, University of Nottingham, Queen's Medical Centre, Nottingham, NG7 2UH, UK.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Allers
mesh_terms: D019843:Archaeal Proteins / Q000378:metabolism; D004261:DNA Replication / Q000235:genetics*; D019641:DNA, Archaeal / Q000032:analysis / Q000096:biosynthesis / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism; D019143:Evolution, Molecular; D019622:Haloferax volcanii / Q000235:genetics* / Q000254:growth & development*; D059014:High-Throughput Nucleotide Sequencing; D059765:Homologous Recombination / Q000235:genetics; D008957:Models, Genetic; D018741:Replication Origin / Q000235:genetics; D013997:Time Factors
chemical_list: D019843:Archaeal Proteins; D019641:DNA, Archaeal; D004268:DNA-Binding Proteins; C117252:RadA protein, archaeal