Mitotic recombination in the rDNA of S. cerevisiae is suppressed by the combined action of DNA topoisomerases I and II

Cell. 1988 Nov 4;55(3):413-25. doi: 10.1016/0092-8674(88)90027-x.


We have found that mitotic recombination within the S. cerevisiae rDNA cluster (200 tandemly repeated 9.1 kb units) is strongly suppressed and that this suppression requires the combined action of DNA topoisomerases I and II. Strains with a null mutation in the TOP1 gene (encoding topoisomerase I) or a ts mutation in the TOP2 gene (encoding topoisomerase II) grown at a semipermissive temperature show 50- to 200-fold higher frequencies of mitotic recombination in rDNA relative to TOP+ controls. Suppression of recombination is specific to the rDNA because the recombination frequency at another tandem array, the CUP1 locus, at a simple HIS4 duplication, or among dispersed repeats (MAT and HML or HMR) is not elevated in top1 or top2 mutants. The high frequency of mitotic recombination within the rDNA cluster in topoisomerase mutants shows that both TOP1 and TOP2 are required for suppression of recombination in this region of the genome.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Blotting, Southern
  • DNA Topoisomerases, Type I / genetics*
  • DNA Topoisomerases, Type I / metabolism
  • DNA Topoisomerases, Type II / genetics*
  • DNA Topoisomerases, Type II / metabolism
  • DNA, Fungal / genetics
  • DNA, Ribosomal / genetics*
  • Deoxyribonuclease EcoRI
  • Genes, Fungal
  • Genotype
  • Meiosis
  • Mitosis
  • Multigene Family
  • Mutation
  • Orotic Acid / analogs & derivatives
  • Orotic Acid / pharmacology
  • Plasmids
  • Polymorphism, Restriction Fragment Length
  • Recombination, Genetic*
  • Saccharomyces cerevisiae / drug effects
  • Saccharomyces cerevisiae / enzymology
  • Saccharomyces cerevisiae / genetics*
  • Sister Chromatid Exchange


  • DNA, Fungal
  • DNA, Ribosomal
  • Orotic Acid
  • 5-fluoroorotic acid
  • Deoxyribonuclease EcoRI
  • DNA Topoisomerases, Type I
  • DNA Topoisomerases, Type II