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rDNA enhancer affects replication initiation and mitotic recombination: Fob1 mediates nucleolytic processing
Martin D Burkhalter1, José M Sogo
1Institute of Cell Biology, Department of Biology, ETH Hönggerberg, CH-8093 Zürich, Switzerland.
Molecular Cell
|August 12, 2004
Summary
The ribosomal DNA enhancer is crucial for blocking replication forks and forming extrachromosomal ribosomal circles in yeast. DNA double-strand breaks and nicks occur at specific sites, with recombination potentially happening outside of S phase.
Area of Science:
- Molecular Biology
- Genetics
- Yeast Genetics
Background:
- Ribosomal DNA (rDNA) arrays are essential for cell function but prone to instability.
- Replication fork dynamics and recombination at rDNA are critical for maintaining genome integrity.
Purpose of the Study:
- To elucidate the role of the ribosomal DNA enhancer in regulating replication initiation and recombination within the rDNA array.
- To investigate the mechanism of extrachromosomal ribosomal circle formation and DNA break occurrence.
Main Methods:
- Utilized Saccharomyces cerevisiae (yeast) strains with tagged rRNA genes.
- Employed nucleotide-resolution mapping to visualize DNA nicks.
- Analyzed replication fork barrier function and DNA double-strand break formation.
Main Results:
- The rDNA enhancer is essential for replication fork barrier function but only modulates replication initiation.
- Enhancer element is required for the formation of monomeric extrachromosomal ribosomal circles.
- DNA double-strand breaks occur at specific sites during stalled replication forks, and nicks coincide with the HOT1 recombination site.
Conclusions:
- The rDNA enhancer plays a critical role in rDNA stability by controlling replication fork progression and recombination.
- Replication fork blocking protein (Fob1) mediates nicks at the HOT1 site, independent of replication.
- Intrachromosomal rDNA recombination may occur independently of DNA replication (S phase).