rDNA enhancer affects replication initiation and mitotic recombination: Fob1 mediates nucleolytic processing independently of replication.
To investigate the influence of the ribosomal DNA enhancer on initiation of replication and recombination at the ribosomal array, we used yeast S. cerevisiae strains with adjacent, tagged rRNA genes. We found that the enhancer is an absolute requirement for replication fork barrier function, while it only modulates initiation of replication. Moreover, the formation of monomeric extrachromosomal ribosomal circles depends on this element. Our data indicate that DNA double-strand breaks occur at specific sites in the parental leading arm of replication forks stalled at the replication fork barrier. Additionally, nicks upstream of the replication fork barrier were visualized by nucleotide-resolution mapping. They coincide with essential sequences of the mitotic hyperrecombination site HOT1, which previously has been determined at ectopic sites. Interestingly, these nicks are strictly dependent on the replication fork blocking-protein (Fob1), but are replication independent, suggesting that intrachromosomal ribosomal DNA recombination may occur outside of S phase.
Burkhalter
Martin D
MD
Institute of Cell Biology, Department of Biology, ETH Hönggerberg, CH-8093 Zürich, Switzerland.
Sogo
José M
JM
D001483:Base Sequence; D001665:Binding Sites; D004249:DNA Damage; D004261:DNA Replication / Q000502:physiology*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004275:DNA, Ribosomal / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D004742:Enhancer Elements, Genetic; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism
C061886:ABF1 protein, S cerevisiae; D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; C105579:FOB1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D004264:DNA Topoisomerases, Type I