Topoisomerase III is essential for accurate nuclear division in Schizosaccharomyces pombe

Abstract

Topoisomerases catalyse changes in the topological state of DNA and are required for many aspects of DNA metabolism. While the functions of topoisomerases I and II in eukaryotes are well established, the role of topoisomerase III remains poorly defined. We have identified a gene in the fission yeast Schizosaccharomyces pombe, designated top3 (+), which shows significant sequence similarity to genes encoding topoisomerase III enzymes in other eukaryotic species. In common with murine TOP3 alpha, but in contrast to Saccharomyces cerevisiae TOP3, the S.pombe top3 (+)gene is essential for long-term cell viability. Fission yeast haploid spores containing a disrupted top3 (+)gene germinate successfully, but then undergo only a limited number of cell divisions. Analysis of these top3 mutants revealed evidence of aberrant mitotic chromosome segregation, including the 'cut' phenotype, where septation is completed prior to nuclear division. Consistent with the existence of an intimate association (originally identified in S.cerevisiae ) between topoisomerase III and DNA helicases of the RecQ family, deletion of the rqh1 (+)gene encoding the only known RecQ helicase in S.pombe suppresses lethality in top3 mutants. This conservation of genetic interaction between two widely diverged yeasts suggests that the RecQ family helicases encoded by the Bloom's and Werner's syndrome genes are likely to act in concert with topoisomerase III isozymes in human cells. Our data are consistent with a model in which the association of a RecQ helicase and topoisomerase III is important for facilitating decatenation of late stage replicons to permit faithful chromosome segregation during anaphase.

Infertility and aneuploidy in mice lacking a type IA DNA topoisomerase IIIβ

“…cellular role of the type IA DNA topoisomerases. Furthermore, any postulate invoking a critical role of a type IA DNA topoisomerase in the resolution of newly replicated chromosome pairs cannot explain the observation that the defects owing to inactivation of these enzymes can be suppressed by mutations in homologous recombination genes (4,(7)(8)(9).…”

“…Concordantly, inactivation of the E. coli recA gene, which is essential for homologous recombination, restores viability of a topA topB double mutant lacking both DNA topoisomerases I and III (4). Earlier studies also showed that the defects of mitotic yeast top3 cells could largely be suppressed by mutations in a helicase of the RecQ family, the Sgs1 protein in S. cerevisiae and the Rqh1 protein in Schizosaccharomyces pombe (6,8,9). Extensive studies of physical and functional interactions between the type IA DNA topoisomerases and RecQ helicases have been carried out (6,(9)(10)(11)(12)(13)(14)(15), prompted by the identification of the human Bloom and Werner syndrome proteins as RecQ helicases (16,17).…”

“…Earlier studies also showed that the defects of mitotic yeast top3 cells could largely be suppressed by mutations in a helicase of the RecQ family, the Sgs1 protein in S. cerevisiae and the Rqh1 protein in Schizosaccharomyces pombe (6,8,9). Extensive studies of physical and functional interactions between the type IA DNA topoisomerases and RecQ helicases have been carried out (6,(9)(10)(11)(12)(13)(14)(15), prompted by the identification of the human Bloom and Werner syndrome proteins as RecQ helicases (16,17). The results of these studies are consistent with a mechanism suggested earlier: a RecQ helicase is involved in the formation of a certain DNA structure, and a type I DNA topoisomerase is required in the subsequent processing of this structure (6).…”

Dual localization of human DNA topoisomerase IIIα to mitochondria and nucleus

“…On the basis of studies in Escherichia coli and the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe, the type IA DNA topoisomerases are most likely involved in chromosome segregation, especially in the resolution of chromosomes that had undergone recombinational repair (4,(44)(45)(46)(47)(48). In animals, the possibility of recombinational repair of mtDNA remains uncertain (reviewed in ref.…”

“…Studies in yeast and mammalian cells have provided strong evidence for physical and functional interaction between type IA DNA topoisomerases and helicases of the RecQ family (45)(46)(47)(54)(55)(56)(57)(58). In mammalian cells, Top3␣ has been suggested to interact with the BLM helicase.…”