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. 2019 May 7;10(5):345. doi: 10.3390/genes10050345

Figure 1.

Figure 1

Brief guide to eukaryotic rDNAome—the genomic organization of the rDNA loci. (a) Structural organization of the 45S rDNA gene cluster (or rRNA transcription unit); the repeating or single clusters of rDNA can be found scattered throughout genome, they form the precursor pre-rRNA since ribonucleases remove spacers and release separate rRNA molecules in nucleolus—the site of ribosome biogenesis to polysome ribosome formation; (b) Structural organization of the 5S rDNA unit (the 5S rDNA can be also dispersed in the genome in many species); (c) 80S eukaryotic ribosome composed of the large subunit (LSU) and the small subunit (SSU) with outlined rRNAs. CP—core promoter, ETS—external transcribed spacer, ICR—internal control region, IE—internal element, IGS—intergenic spacer, ITS1, ITS2—internal transcribed spacer 1 and 2, RNA Pol I and III—RNA polymerase I and III, LSU—large (ribosomal) subunit, nt—nucleotides, NTS—non-transcribed spacer, SSU—small subunit, TIS—transcription initiation site, TTTT—polyT transcription termination site, UCE—upstream control element.