A new nomenclature of group I introns in ribosomal DNA

• Published in: RNA (Cambridge) Vol. 7; no. 7; pp. 935 - 936
• Main Authors: JOHANSEN, STEINAR, HAUGEN, PEIK
• Format: Journal Article
• Language: English
• Published: United States Cambridge University Press 01-07-2001
• Subjects: DNA, Ribosomal - genetics; Fuligo septica; Introns; Lecanora dispersa; Letter; LETTER TO THE EDITOR; Molecular Sequence Data; rDNA; rRNA; SSU rDNA; Terminology as Topic
• ISSN: 1355-8382; 1469-9001
• DOI: 10.1017/S1355838201010500

The current nomenclature system of group I introns
(see Cech, 1988; Michel & Westhof, 1990) has become
insufficient to distinguish and categorize the complex
collection of more than 900 group I introns in ribosomal
DNA (rDNA) of nuclear, mitochondrial, chloroplast, and
eubacterial genomes (http://www.rna.icmb.utexas.edu/; GenBank;
our unpubl. results) in a rational way. The majority of
these group I introns (∼750) are found in nuclear rDNA
of fungi and protists, but the distribution appears highly
scattered since most species analyzed lack introns. Many
of the rDNA introns are optional among strains of a particular
species or between closely related species, and some have
been shown in experimental settings to be true mobile genetic
elements (see Belfort & Roberts, 1997). All group I
rDNA introns are found at a limited number of insertion
sites (∼75) in highly conserved regions of the small
subunit (SSU) and large subunit (LSU) rRNA genes, and some
of these sites (∼10) are shared by introns from the
nuclei, mitochondria, or chloroplasts. There are numerous
examples of multiple group I introns in a single rRNA gene,
and as many as eight nuclear introns have been noted in
the SSU rDNA of the lichen ascomycete Lecanora dispersa
(accession number L37734) and in the LSU rDNA of the myxomycete
Fuligo septica (our unpubl. results). Finally,
group I introns that occupy the same site in rDNA, but
in distantly related hosts, tend to share a number of structural
features as well as high levels of primary sequence similarities
compared to introns at different insertion sites (e.g., Suh et al., 1999).