title: Topoisomerase I plays a critical role in suppressing genome instability at a highly transcribed G-quadruplex-forming sequence.
abstract: G-quadruplex or G4 DNA is a non-B secondary DNA structure that comprises a stacked array of guanine-quartets. Cellular processes such as transcription and replication can be hindered by unresolved DNA secondary structures potentially endangering genome maintenance. As G4-forming sequences are highly frequent throughout eukaryotic genomes, it is important to define what factors contribute to a G4 motif becoming a hotspot of genome instability. Using a genetic assay in Saccharomyces cerevisiae, we previously demonstrated that a potential G4-forming sequence derived from a guanine-run containing immunoglobulin switch Mu (Sμ) region becomes highly unstable when actively transcribed. Here we describe assays designed to survey spontaneous genome rearrangements initiated at the Sμ sequence in the context of large genomic areas. We demonstrate that, in the absence of Top1, a G4 DNA-forming sequence becomes a strong hotspot of gross chromosomal rearrangements and loss of heterozygosity associated with mitotic recombination within the ∼ 20 kb or ∼ 100 kb regions of yeast chromosome V or III, respectively. Transcription confers a critical strand bias since genome rearrangements at the G4-forming Sμ are elevated only when the guanine-runs are located on the non-transcribed strand. The direction of replication and transcription, when in a head-on orientation, further contribute to the elevated genome instability at a potential G4 DNA-forming sequence. The implications of our identification of Top1 as a critical factor in suppression of instability associated with potential G4 DNA-forming sequences are discussed.
authors.affiliation: Department of Microbiology and Molecular Genetics, University of Texas Health Science Center at Houston, Houston, Texas, United States of America.
authors.forename: Puja
authors.initials: P
authors.lastname: Yadav
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Victoria
authors.initials: V
authors.lastname: Harcy
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Juan Lucas
authors.initials: JL
authors.lastname: Argueso
authors.affiliation: Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, United States of America.
authors.forename: Margaret
authors.initials: M
authors.lastname: Dominska
authors.affiliation: Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, United States of America.
authors.forename: Sue
authors.initials: S
authors.lastname: Jinks-Robertson
authors.affiliation: Department of Microbiology and Molecular Genetics, University of Texas Health Science Center at Houston, Houston, Texas, United States of America.
authors.forename: Nayun
authors.initials: N
authors.lastname: Kim
mesh_terms: D004264:DNA Topoisomerases, Type I / Q000502:physiology*; D054856:G-Quadruplexes; D017353:Gene Deletion; D042822:Genomic Instability; D006147:Guanine / Q000378:metabolism; D007134:Immunoglobulin Switch Region / Q000235:genetics; D055029:Inverted Repeat Sequences; D030781:Organisms, Genetically Modified; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000235:genetics; D016615:Telomere / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D006147:Guanine; D004264:DNA Topoisomerases, Type I