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J Bacteriol, July 1998, p. 3635-3643, Vol. 180, No. 14
Laboratory of Marine Microbiology, Division
of Applied Bioscience, Graduate School of Agriculture, Kyoto
University, Kyoto 606-8502, Japan
Received 25 November 1997/Accepted 11 May 1998
The single rRNA operon (arnS-arnL) of the
hyperthermophilic archaeon Aeropyrum pernix K1 was
sequenced. The DNA sequence data and detailed RNA analyses
disclosed an unusual feature: the presence of three introns at hitherto
undescribed insertion positions within the rRNA genes. The
699-nucleotide (nt) intron I
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Copyright © 1998, American Society for Microbiology. All rights reserved.
Molecular Characterization and Postsplicing Fate of Three Introns
within the Single rRNA Operon of the Hyperthermophilic Archaeon
Aeropyrum pernix K1
was located at position 908 (Escherichia coli numbering [H. F. Noller, Annu. Rev.
Biochem. 53:119-162, 1984]) of the 16S rRNA, while the 202-nt intron
I
and 575-nt intron I
were located at positions 1085 and 1927 (E. coli numbering), respectively, of the 23S
rRNA. They were located within highly conserved sites which have been
implicated as crucial for rRNA function in E. coli. All
three introns were remarkably AT rich (41.5 to 43.1 mol% G+C) compared
with the mature rRNAs (67.7 and 69.2 mol% G+C for 16S and 23S rRNAs,
respectively). No obvious primary sequence similarities were detected
among them. After splicing from rRNA transcripts in vivo, a large
quantity of intronic RNAs were stably retained in the linear monomeric form, whereas a trace of topoisomeric RNA molecules also
appeared, as characterized by their behavior in two-dimensional gel
electrophoresis. Secondary structural models of the I
-, I
-, and
I
-containing rRNA precursors agree with the bulge-helix-bulge motif.
Two of the introns, I
and I
, contained open reading frames whose
protein translation exhibited no overall similarity with proteins
reported so far. However, both share a LAGLI-DADG motif characteristic of homing endonucleases.
*
Corresponding author. Mailing address: Laboratory of
Marine Microbiology, Division of Applied Bioscience, Graduate School of
Agriculture, Kyoto University, Kyoto 606-8502, Japan. Phone: 81-75-753-6219. Fax: 81-75-753-6226. E-mail:
j54718{at}sakura.kudpc.kyoto-u.ac.jp.
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