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Journal of Bacteriology, June 1999, p. 3445-3451, Vol. 181, No. 11
Division of General Genetics, Department of
Biology, University of Oslo, 0315 Oslo, Norway
Received 26 May 1998/Accepted 24 March 1999
Based on the findings that plastids and cyanobacteria have similar
group I introns inserted into tRNAUAALeu genes,
these introns have been suggested to be immobile and of ancient origin.
In contrast, recent evidence suggests lateral transfer of
cyanobacterial group I introns located in
tRNAUAALeu genes. In light of these new findings,
we have readdressed the evolution and lateral transfer of
tRNAUAALeu group I introns in cyanobacteral
radiation. We determined the presence of introns in 38 different
strains, representing the major cyanobacterial lineages, and
characterized the introns in 22 of the strains. Notably, two of these
strains have two tRNAUAALeu genes, with each of
these genes interrupted by introns, while three of the strains have
both interrupted and uninterrupted genes. Two evolutionary distinct
clusters of tRNA genes, with the genes interrupted by introns
belonging to two distinct intron clusters, were identified. We also
compared 16S rDNA and intron evolution for both closely and distantly
related strains. The distribution of the introns in the clustered
groups, as defined from 16S rDNA analysis, indicates relatively recent
gain and/or loss of the introns in some of these lineages. The
comparative analysis also suggests differences in the phylogenetic
trees for 16S rDNA and the tRNAUAALeu group I
introns. Taken together, our results show that the evolution of the
intron is considerably more complex than previous studies found to be
the case. We discuss, based on our results, evolutionary models
involving lateral intron transfer and models involving differential
loss of the intron.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Complex Evolutionary Patterns of
tRNAUAALeu Group I Introns in
Cyanobacterial Radiation
*
Corresponding author. Present address for K. Rudi:
MATFORSK Norwegian Food Research Institute, Osloveien 1, 1430 Ås,
Norway. Phone: 47.64.97.02.66. Fax: 47.64.97.03.33. E-mail:
knut.rudi{at}matforsk.no. Mailing address for K. S. Jakobsen: Division of General Genetics, Department of Biology,
University of Oslo, P.O. Box 1031 Blindern, 0315, Oslo, Norway.
Phone: 47.22.85.46.02. Fax:
47.22.85.46.05. E-mail:
kjetill.jakobsen{at}bio.uio.no.
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