Ribosomal DNA

The gene segment of eukaryotic rDNA contains 18S, 5.8S, and 28S tracts and forms a tandem repetitive cluster; the 5S rDNA is coded separately. NTS, nontranscribed spacer, ETS, external transcribed spacer, ITS, internal transcribed spacers 1 and 2, numbered from 5' end.
Nucleolus with pre-rRNA components called Introns and Exons.

Ribosomal DNA (rDNA) is a DNA sequence that codes for ribosomal RNA. These sequences regulate transcription initiation and amplification, and contain both transcribed and non-transcribed spacer segments.

In the human genome there are 5 chromosomes with nucleolus organizer regions: the acrocentric chromosomes 13 (RNR1), 14 (RNR2), 15 (RNR3), 21 (RNR4) and 22 (RNR5). The genes that are responsible for encoding the various sub-units of rRNA are located across multiple chromosomes in humans. But the genes that encode for rRNA are highly conserved across the domains, with only the copy numbers involved for the genes having varying numbers per species.[1] In Bacteria, Archaea, and chloroplasts the rRNA is composed of different (smaller) units, the large (23S) ribosomal RNA, 16S ribosomal RNA and 5S rRNA. The 16S rRNA is widely used for phylogenetic studies.[2]

  1. ^ Cite error: The named reference Rob was invoked but never defined (see the help page).
  2. ^ Weisburg WG, Barns SM, Pelletier DA, Lane DJ (January 1991). "16S ribosomal DNA amplification for phylogenetic study". Journal of Bacteriology. 173 (2): 697–703. doi:10.1128/jb.173.2.697-703.1991. PMC 207061. PMID 1987160.

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