The gene that produces the precursor RNA transcript to the three largest structural rRNA molecules (rDNA) is present in multiple copies and organized into gene clusters. The 10 human rDNA clusters represent <0.5% of the diploid human genome but are critically important for cellular viability. Individual genes within rDNA clusters possess very high levels of sequence identity with respect to eac...

The rDNA genes are transcribed by RNA polymerase I to make structural RNAs for ribosomes. Hundreds of rDNA genes are typically arranged in an array that spans megabase pairs of DNA. These arrays are the major sites of transcription in growing cells, accounting for as much as 50% of RNA synthesis. The repetitive rDNA arrays are thought to use heterochromatic gene silencing as a mechanism for met...

The abundant rDNA minichromosome of Tetrahymena thermophila is generated by a series of developmentally controlled processing steps, termed rDNA maturation, during the formation of the new macronucleus in conjugating cells. rDNA maturation involves excision of a region encoding the single copy rRNA gene (rDNA) from its germline location, rearrangement of the rDNA into a palindromic minichromoso...

BACKGROUND AND AIMS Brassica napus (AACC, 2n = 38, oilseed rape) is a relatively recent allotetraploid species derived from the putative progenitor diploid species Brassica rapa (AA, 2n = 20) and Brassica oleracea (CC, 2n = 18). To determine the influence of intensive breeding conditions on the evolution of its genome, we analysed structure and copy number of rDNA in 21 cultivars of B. napus, r...

Concerted evolution maintains at near identity the hundreds of tandemly arrayed ribosomal RNA (rRNA) genes and their spacers present in any eukaryote. Few comprehensive attempts have been made to directly measure the identity between the rDNA units. We used the original sequencing reads (trace archives) available through the whole-genome shotgun sequencing projects of 12 Drosophila species to l...

Phylogenetic analysis of a 500 bp fragment of the secA gene has been performed on 35 phytoplasma isolates representing 10 of the 16S rDNA groups. The lineages obtained coincide with those delineated by 16S rDNA phylogenetic analysis but much greater genetic variability was evident. In addition, phylogenetic analysis based on part of the 23S rDNA gene combined with T-RFLP (terminal restriction f...

Loss of c-MYC is required for downregulation of ribosomal RNA (rRNA) gene (rDNA) transcription by RNA Polymerase I (Pol I) during granulocyte differentiation. Here, we demonstrate a robust reduction of Pol I loading onto rDNA that along with a depletion of the MYC target gene upstream binding factor (UBF) and a switch from epigenetically active to silent rDNA accompanies this MYC reduction. We ...

Ribosomal RNA gene (rDNA) copy number variation modulates heterochromatin formation and influences the expression of a large fraction of the Drosophila genome. This discovery, along with the link between rDNA, aging, and disease, high-lights the importance of understanding how natural rDNA copy number variation arises. Pursuing the relationship between rDNA expression and stability, we have dis...

5S ribosomal RNA gene repeats are arranged in heterochromatic arrays (5S rDNA) situated near the centromeres of Arabidopsis chromosomes. The chromatin remodeling factor DDM1 is known to maintain 5S rDNA methylation patterns while silencing transcription through 5S rDNA intergenic spacers (IGS). We mapped small-interfering RNAs (siRNA) to a composite 5S rDNA repeat, revealing a high density of s...