Epigenetic silencing of a fraction of ribosomal DNA (rDNA) requires association of the nucleolar chromatin-remodelling complex NoRC to 150-250 nucleotide RNAs (pRNA) that originate from an RNA polymerase I promoter located in the intergenic spacer separating rDNA repeats. Here, we show that NoRC-associated pRNA is transcribed from a sub-fraction of hypomethylated rRNA genes during mid S phase, ...

The genome is composed not only of genes but also of several noncoding functional elements (NOCs/ncFE, here I use NOCs), such as transcriptional promoters, enhancers, replication origins, centromeres and telomeres. rDNA has both gene and NOC characteristics. Thus, the rDNA encodes ribosomal RNAs, components of the ribosomes, that account for approximately 80% of the total RNA in a cell. However...

We compared nucleotide sequences of the transcription-initiation region of five mouse ribosomal DNA (rDNA) clones. Two clones were isolated from Japanese wild mice, Mus musculus molossinus, and the other three from BALB/c mice originating in M. m. domesticus. Two BALB/c clones that are derived from the same chromosome are very similar, suggesting the occurrence of intrachromosomal homogenizatio...

Silencing within the yeast ribosomal DNA (rDNA) repeats protects the integrity of this highly repetitive array by inhibiting hyperrecombination and repressing transcription from foreign promoters. Using affinity purification combined with highly sensitive mixture mass spectrometry, we have analyzed the protein interaction network involved in suppressing homologous recombination within the rDNA ...

The genes encoding ribosomal RNA are the most abundant in the eukaryotic genome. They reside in tandem repetitive clusters, in some cases totaling hundreds of copies. Due to their repetitive structure, ribosomal RNA genes (rDNA) are easily lost by recombination events within the repeated cluster. We previously identified a unique gene amplification system driven by unequal sister-chromatid reco...

To examine relationships among spirotrich ciliates using multi-locus sequence analyses and to provide preliminary insights into molecular diversity within species, we sequenced the small subunit rDNA (SSU rDNA), 5.8S rDNA, alpha-tubulin and the internally transcribed spacer regions (ITS1 and ITS2) of the rDNA genes from seven choreotrich (Class: Spirotrichea) and three oligotrich (Class: Spirot...

Major eukaryotic genomic elements, including the ribosomal DNA (rDNA), are composed of repeated sequences with well-defined copy numbers that must be maintained by regulated recombination. Although mechanisms that instigate rDNA recombination have been identified, none are directional and they therefore cannot explain precise repeat number control. Here, we show that yeast lacking histone chape...

Ribosome biogenesis is essential for cell growth and proliferation and is commonly elevated in cancer. Accordingly, numerous oncogene and tumor suppressor signaling pathways target rRNA synthesis. In breast cancer, non-canonical Wnt signaling by Wnt5a has been reported to antagonize tumor growth. Here, we show that Wnt5a rapidly represses rDNA gene transcription in breast cancer cells and gener...

Ribosomal RNA gene (rDNA) loci of Russian Mus musculus musculus and of Japanese Mus musuculus molossinus were mapped by double color FISH. The total number of rDNA loci was varied from 5 to 12, although the loci on chromosomes 12, 15, 16, 18, and 19 were common to all mice examined. Instead, polymorphisms of the rDNA loci were found on chromosomes 1, 5, 8, 9, 10, 11, 13 and 17. The novel rDNA l...