Editor: Colin Berry
Ribosomal RNA genes in eukaryotic microorganisms: witnesses of phylogeny?
Article first published online: 31 OCT 2009
© 2009 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved
FEMS Microbiology Reviews
Volume 34, Issue 1, pages 59–86, January 2010
How to Cite
Torres-Machorro, A. L., Hernández, R., Cevallos, A. M. and López-Villaseñor, I. (2010), Ribosomal RNA genes in eukaryotic microorganisms: witnesses of phylogeny?. FEMS Microbiology Reviews, 34: 59–86. doi: 10.1111/j.1574-6976.2009.00196.x
- Issue published online: 10 DEC 2009
- Article first published online: 31 OCT 2009
- Received 4 September 2009; revised 25 October 2009; accepted 27 October 2009.Final version published online 23 November 2009.
- 5S rRNA;
- unicellular eukaryote;
- ribosomal cistron organization;
- extrachromosomal gene;
- repeated sequence
The study of genomic organization and regulatory elements of rRNA genes in metazoan paradigmatic organisms has led to the most accepted model of rRNA gene organization in eukaryotes. Nevertheless, the rRNA genes of microbial eukaryotes have also been studied in considerable detail and their atypical structures have been considered as exceptions. However, it is likely that these organisms have preserved variations in the organization of a versatile gene that may be seen as living records of evolution. Here, we review the organization of the main rRNA transcription unit (rDNA) and the 5S rRNA genes (5S rDNA). These genes are reiterated in the genome of microbial eukaryotes and may be coded alone, in tandem repeats, linked to each other or linked to other genes. They may be found in the chromosome or extrachromosomally in linear or circular units. rDNA coding regions may contain introns, sequence insertions, protein-coding genes or additional spacers. The 5S rDNA can be found in tandem repeats or genetically linked to genes transcribed by RNA polymerases I, II or III. Available information from about a hundred microbial eukaryotes was used to review the unexpected diversity in the genomic organization of rRNA genes.