title: Top2 and Sgs1-Top3 Act Redundantly to Ensure rDNA Replication Termination.
abstract: Faithful DNA replication with correct termination is essential for genome stability and transmission of genetic information. Here we have investigated the potential roles of Topoisomerase II (Top2) and the RecQ helicase Sgs1 during late stages of replication. We find that cells lacking Top2 and Sgs1 (or Top3) display two different characteristics during late S/G2 phase, checkpoint activation and accumulation of asymmetric X-structures, which are both independent of homologous recombination. Our data demonstrate that checkpoint activation is caused by a DNA structure formed at the strongest rDNA replication fork barrier (RFB) during replication termination, and consistently, checkpoint activation is dependent on the RFB binding protein, Fob1. In contrast, asymmetric X-structures are formed independent of Fob1 at less strong rDNA replication fork barriers. However, both checkpoint activation and formation of asymmetric X-structures are sensitive to conditions, which facilitate fork merging and progression of replication forks through replication fork barriers. Our data are consistent with a redundant role of Top2 and Sgs1 together with Top3 (Sgs1-Top3) in replication fork merging at rDNA barriers. At RFB either Top2 or Sgs1-Top3 is essential to prevent formation of a checkpoint activating DNA structure during termination, but at less strong rDNA barriers absence of the enzymes merely delays replication fork merging, causing an accumulation of asymmetric termination structures, which are solved over time.
authors.affiliation: Laboratory of Genome Research, Department of Molecular Biology and Genetics, Aarhus University, Aarhus C, Denmark.
authors.forename: Kamilla
authors.initials: K
authors.lastname: Mundbjerg
authors.affiliation: Laboratory of Genome Research, Department of Molecular Biology and Genetics, Aarhus University, Aarhus C, Denmark.|Department of Cellular and Molecular Medicine, University of Copenhagen, Copenhagen N, Denmark.
authors.forename: Signe W
authors.initials: SW
authors.lastname: Jørgensen
authors.affiliation: Laboratory of Genome Research, Department of Molecular Biology and Genetics, Aarhus University, Aarhus C, Denmark.|Department of Molecular Medicine, Aarhus University Hospital, Aarhus N, Denmark.
authors.forename: Jacob
authors.initials: J
authors.lastname: Fredsøe
authors.affiliation: Laboratory of Genome Research, Department of Molecular Biology and Genetics, Aarhus University, Aarhus C, Denmark.
authors.forename: Ida
authors.initials: I
authors.lastname: Nielsen
authors.affiliation: Laboratory of Genome Research, Department of Molecular Biology and Genetics, Aarhus University, Aarhus C, Denmark.
authors.forename: Jakob Madsen
authors.initials: JM
authors.lastname: Pedersen
authors.affiliation: Laboratory of Genome Research, Department of Molecular Biology and Genetics, Aarhus University, Aarhus C, Denmark.
authors.forename: Iben Bach
authors.initials: IB
authors.lastname: Bentsen
authors.affiliation: Department of Biology, University of Copenhagen, Copenhagen N, Denmark.
authors.forename: Michael
authors.initials: M
authors.lastname: Lisby
authors.affiliation: Laboratory of Genome Research, Department of Molecular Biology and Genetics, Aarhus University, Aarhus C, Denmark.
authors.forename: Lotte
authors.initials: L
authors.lastname: Bjergbaek
authors.affiliation: Laboratory of Genome Research, Department of Molecular Biology and Genetics, Aarhus University, Aarhus C, Denmark.
authors.forename: Anni H
authors.initials: AH
authors.lastname: Andersen
mesh_terms: D015825:Chromosomes, Fungal / Q000235:genetics; D004249:DNA Damage / Q000235:genetics; D004261:DNA Replication / Q000235:genetics*; D004264:DNA Topoisomerases, Type I / Q000235:genetics*; D004275:DNA, Ribosomal / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D042822:Genomic Instability; D053484:RecQ Helicases / Q000235:genetics*; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; C090472:SGS1 protein, S cerevisiae; D053484:RecQ Helicases; D004264:DNA Topoisomerases, Type I