title: DNA topoisomerase III localizes to centromeres and affects centromeric CENP-A levels in fission yeast.
abstract: Centromeres are specialized chromatin regions marked by the presence of nucleosomes containing the centromere-specific histone H3 variant CENP-A, which is essential for chromosome segregation. Assembly and disassembly of nucleosomes is intimately linked to DNA topology, and DNA topoisomerases have previously been implicated in the dynamics of canonical H3 nucleosomes. Here we show that Schizosaccharomyces pombe Top3 and its partner Rqh1 are involved in controlling the levels of CENP-A(Cnp1) at centromeres. Both top3 and rqh1 mutants display defects in chromosome segregation. Using chromatin immunoprecipitation and tiling microarrays, we show that Top3, unlike Top1 and Top2, is highly enriched at centromeric central domains, demonstrating that Top3 is the major topoisomerase in this region. Moreover, centromeric Top3 occupancy positively correlates with CENP-A(Cnp1) occupancy. Intriguingly, both top3 and rqh1 mutants display increased relative enrichment of CENP-A(Cnp1) at centromeric central domains. Thus, Top3 and Rqh1 normally limit the levels of CENP-A(Cnp1) in this region. This new role is independent of the established function of Top3 and Rqh1 in homologous recombination downstream of Rad51. Therefore, we hypothesize that the Top3-Rqh1 complex has an important role in controlling centromere DNA topology, which in turn affects the dynamics of CENP-A(Cnp1) nucleosomes.
authors.affiliation: Center for Biosciences, Department of Biosciences and Nutrition, Karolinska Institutet, Huddinge, Sweden.
authors.forename: Ulrika
authors.initials: U
authors.lastname: Norman-Axelsson
authors.forename: Mickaël
authors.initials: M
authors.lastname: Durand-Dubief
authors.forename: Punit
authors.initials: P
authors.lastname: Prasad
authors.forename: Karl
authors.initials: K
authors.lastname: Ekwall
mesh_terms: D002503:Centromere / Q000235:genetics / Q000648:ultrastructure; D002843:Chromatin / Q000235:genetics / Q000648:ultrastructure; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism; D020090:Chromosome Segregation / Q000235:genetics; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism; D006657:Histones / Q000235:genetics / Q000378:metabolism; D059765:Homologous Recombination; D018386:Kinetochores / Q000648:ultrastructure; D009707:Nucleosomes / Q000235:genetics; D051135:Rad51 Recombinase / Q000235:genetics; D012568:Schizosaccharomyces / Q000235:genetics / Q000378:metabolism; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; C410349:Cnp1 protein, S pombe; D006657:Histones; D009707:Nucleosomes; D029702:Schizosaccharomyces pombe Proteins; D051135:Rad51 Recombinase; D004265:DNA Helicases; C106462:Rqh1 protein, S pombe; D004264:DNA Topoisomerases, Type I