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Journal of Bacteriology, September 1998, p. 4804-4813, Vol. 180, No. 18
Department of Biochemistry and Molecular
Biology, University of British Columbia, Vancouver, British
Columbia V6T 1Z3, Canada
Received 12 January 1998/Accepted 22 April 1998
The genome of the halophilic archaeon Haloarcula
marismortui contains two rRNA operons designated rrnA
and rrnB. Genomic clones of the two operons and their
flanking regions have been sequenced, and primary transcripts and
processing intermediates derived from each operon have been
characterized. The 16S, 23S, and 5S genes from the two operons were
found to differ at 74 of 1,472 positions, 39 of 2,922 positions, and 2 of 122 positions, respectively. This degree of sequence divergence for
multicopy (paralogous) rRNA genes was 10- to 50-fold or more higher
than anticipated. The two operons exhibit other profound differences
that include (i) the presence in rrnA and the absence in
rrnB of tRNAAla and tRNACys genes
in the intergenic and distal regions, respectively, (ii) divergent 5'
flanking sequences, and (iii) distinct pathways for processing and
maturation of 16S rRNA. Processing and maturation of 16S and 23S rRNA
from rrnA operon transcripts and of 23S rRNA from
rrnB operon transcripts follow the canonical halophilic
pathway, whereas maturation of 16S rRNA from rrnB operon
transcripts follows an unusual and different pathway that is apparently
devoid of any 5' processing intermediate.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Transcription Analysis of Two Disparate rRNA
Operons in the Halophilic Archaeon Haloarcula
marismortui
*
Corresponding author. Mailing address: Department of
Biochemistry and Molecular Biology, University of British Columbia,
2146 Health Sciences Mall, Vancouver, BC V6T 123, Canada. Phone: (604) 822-5975. Fax: (604) 822-5227. E-mail:
pdp1{at}unixg.ubc.ca.
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