title: Isolation of mutants of Saccharomyces cerevisiae requiring DNA topoisomerase I.
abstract: Despite evidence that DNA topoisomerase I is required to relieve torsional stress during DNA replication and transcription, yeast strains with a top1 null mutation are viable and display no gross defects in DNA or RNA synthesis, possibly because other proteins provide overlapping functions. We isolated mutants whose inviablility or growth defect is relieved when TOP1 is expressed [trf mutants (topoisomerase one-requiring function)]. The TRF genes define at least four complementation groups. TRF3 is allelic to TOP2. TRF1 is allelic to HPR1, previously shown to be homologous to TOP1 over two short regions. TRF4 encodes a novel 584-amino acid protein with homology to the N-terminus of Saccharomyces cerevisiae topo I. Like top1 mutants, trf4 mutants have elevated rDNA recombination and fail to shut off RNA polymerase II transcription in stationary phase. trf4 null mutants are cs for viability, display reduced expression of GAL1 and Cell Cycle Box UAS::LacZ fusions, and are inviable in combination with trfI null mutants, indicating that both proteins may share a common function with DNA topoisomerase I. The existence of multiple TRF complementation groups suggests that not all biological functions of topo I can be carried out by topo II.
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco 94143, USA.
authors.forename: B U
authors.initials: BU
authors.lastname: Sadoff
authors.forename: S
authors.initials: S
authors.lastname: Heath-Pagliuso
authors.forename: I B
authors.initials: IB
authors.lastname: Castaño
authors.forename: Y
authors.initials: Y
authors.lastname: Zhu
authors.forename: F S
authors.initials: FS
authors.lastname: Kieff
authors.forename: M F
authors.initials: MF
authors.lastname: Christman
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D001483:Base Sequence; D003433:Crosses, Genetic; D004261:DNA Replication; D004264:DNA Topoisomerases, Type I / Q000235:genetics* / Q000378:metabolism*; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D005800:Genes, Fungal; D005804:Genes, Lethal; D005816:Genetic Complementation Test; D005838:Genotype; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010957:Plasmids; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic
chemical_list: D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II