The Saccharomyces Pif1p DNA helicase and the highly related Rrm3p have opposite effects on replication fork progression in ribosomal DNA

Cell. 2000 Feb 18;100(4):479-89. doi: 10.1016/s0092-8674(00)80683-2.


Replication of Saccharomyces ribosomal DNA (rDNA) proceeds bidirectionally from origins in a subset of the approximately 150 tandem repeats, but the leftward-moving fork stops when it encounters the replication fork barrier (RFB). The Pif1p helicase and the highly related Rrm3p were rDNA associated in vivo. Both proteins affected rDNA replication but had opposing effects on fork progression. Pif1p helped maintain the RFB. Rrm3p appears to be the replicative helicase for rDNA as it acted catalytically to promote fork progression throughout the rDNA. Loss of Rrm3p increased rDNA breakage and accumulation of rDNA circles, whereas breakage and circles were less common in pif1 cells. These data support a model in which replication fork pausing causes breakage and recombination in the rDNA.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Base Sequence
  • Catalysis
  • DNA Helicases / genetics
  • DNA Helicases / metabolism*
  • DNA Replication*
  • DNA, Fungal / biosynthesis*
  • DNA, Ribosomal / biosynthesis*
  • DNA-Binding Proteins / metabolism
  • Fungal Proteins / genetics
  • Fungal Proteins / metabolism
  • Molecular Sequence Data
  • Rad52 DNA Repair and Recombination Protein
  • Saccharomyces cerevisiae / enzymology*
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae Proteins*


  • DNA, Fungal
  • DNA, Ribosomal
  • DNA-Binding Proteins
  • Fungal Proteins
  • RAD52 protein, S cerevisiae
  • Rad52 DNA Repair and Recombination Protein
  • Saccharomyces cerevisiae Proteins
  • PIF1 protein, S cerevisiae
  • DNA Helicases

Associated data

  • GENBANK/U00062
  • PDB/S46744