title: The top3(+) gene is essential in Schizosaccharomyces pombe and the lethality associated with its loss is caused by Rad12 helicase activity.
abstract: The topoisomerase III gene ( top3 (+)) from Schizosaccharomyces pombe was isolated and a targeted gene disruption ( top3 :: kan (R)) was used to make a diploid strain heterozygous for top3 (+). The diploid was sporulated and the top3 :: kan (R)spores went through four to eight cell divisions before arresting as elongated, predominantly binucleated cells with incompletely segregated chromosomes. This demonstrates that top3 (+)is essential for vegetative growth in fission yeast. The aberrant chromosomal segregation seen in top3 :: kan (R)cells is unlike the 'cut' phenotype seen in mitosis-defective mutants and so we refer to this phenotype as 'torn'. A deletion mutant, rad12-hd ( rad12 is a homolog of Saccharomyces cerevisiae SGS1), partially suppressed the lethality of top3 mutants. A point mutant, rad12-K547I, which presumably eliminates helicase activity, also suppresses the lethality of top3 mutants, demonstrating that the lethality seen in top3 (-)cells is most likely caused by the helicase activity of Rad12. This double mutant grows very slowly and has much lower viability compared to rad12-hd top3 :: kan (R)cells, implying that the helicase activity of Rad12 is not the only cause of top3 (-)lethality. The low viability of rad12 (-) top3 (-)mutants compared with rad12 single mutants suggests that Top3 also functions independently of Rad12.
authors.affiliation: Division of Environmental Sciences, Joseph Mailman School of Public Health, New York, NY 10032, USA.
authors.forename: M
authors.initials: M
authors.lastname: Maftahi
authors.forename: C S
authors.initials: CS
authors.lastname: Han
authors.forename: L D
authors.initials: LD
authors.lastname: Langston
authors.forename: J C
authors.initials: JC
authors.lastname: Hope
authors.forename: N
authors.initials: N
authors.lastname: Zigouras
authors.forename: G A
authors.initials: GA
authors.lastname: Freyer
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002455:Cell Division; D003001:Cloning, Molecular; D004265:DNA Helicases / Q000378:metabolism*; D004264:DNA Topoisomerases, Type I / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D004171:Diploidy; D017353:Gene Deletion; D020043:Genes, Essential; D005800:Genes, Fungal; D005804:Genes, Lethal; D005838:Genotype; D006579:Heterozygote; D006801:Humans; D008938:Mitosis; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010641:Phenotype; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D012568:Schizosaccharomyces / Q000201:enzymology / Q000235:genetics* / Q000502:physiology; D029702:Schizosaccharomyces pombe Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013172:Spores, Fungal
chemical_list: D018797:Cell Cycle Proteins; D011994:Recombinant Proteins; D029702:Schizosaccharomyces pombe Proteins; D004265:DNA Helicases; C106462:Rqh1 protein, S pombe; D004264:DNA Topoisomerases, Type I