Expansion and contraction of ribosomal DNA repeats in Saccharomyces cerevisiae: requirment of replication fork blocking (Fob1) Protein and the role of RNA polymerase I

Article Abstract:

Saccharomyces cerevisiae has about 150 copies of rDNA in tandem repeats. Without an essential subunit of RNA polymerase I (Pol I) in rpa135 deletion mutants, a gradual decrease in rDNA repeat number is triggered. Replacing the missing RPA135 gene brings a gradual increase in repeat number until it returns to the normal level. Gene FOB1 is required for the decrease and the increase of rDNA repeats. DNA replication fork blockage seems to bring on recombination and have an essential function in rDNA sequence homogenization and expansion/contraction. RNA Pol I seems to dominate or repeat numbers, perhaps by stabilizing rDNA with normal repeat numbers as a stable nucleolar structure.

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SIR2 regulates recombination between different rDNA repeats, but not recombination within individual rRNA genes in yeast

Article Abstract:

SIR2- dependent chromatin structures inhibit access and/ or function of recombination machinery in rDNA. Various experiments conclude that SIR2 prevents unequal sister-chromatid recombination by forming special cohesin structures without significant effects on recombinational events within individual rDNA genes.

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Cdc14 phosphatase induces rDNA condensation and resolves cohesin-independent cohesion during budding yeast anaphase

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The protease separase triggers chromosome segregation by cleaving the chromosomal cohesin complex during budding yeast anaphase. A temporal order to chromosome segregation could be introduced by the Cdc14-dependent sister chromatid resolution at the rDNA.

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