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Title
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Self-splicing introns in tRNA genes of widely divergent bacteria.
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Authors
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B.Reinhold-Hurek,
D.A.Shub.
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Ref.
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Nature, 1992,
357,
173-176.
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PubMed id
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Abstract
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The organization of eukaryotic genes into exons separated by introns has been
considered as a primordial arrangement but because it does not exist in
eubacterial genomes it may be that introns are relatively recent acquisitions. A
self-splicing group I intron has been found in cyanobacteria at the same
position of the same gene (that encoding leucyl transfer RNA, UAA anticodon) as
a similar group I intron of chloroplasts, which indicates that this intron
predates the invasion of eukaryotic cells by cyanobacterial endosymbionts. But
it is not clear from this isolated example whether introns are more generally
present in different genes or in more diverse branches of the eubacteria. Many
mitochondria have intron-rich genomes and were probably derived from the alpha
subgroup of the purple bacteria (or Proteobacteria), so ancient introns might
also have been retained in these bacteria. We describe here the discovery of two
small (237 and 205 nucleotides) self-splicing group I introns in members of two
proteobacterial subgroups, Agrobacterium tumefaciens (alpha) and Azoarcus sp.
(beta). The introns are inserted in genes for tRNA(Arg) and tRNA(Ile),
respectively, after the third anticodon nucleotide. Their occurrence in
different genes of phylogenetically diverse bacteria indicates that group I
introns have a widespread distribution among eubacteria.
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