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Journal of Bacteriology, September 1998, p. 4804-4813, Vol. 180, No. 18
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

Patrick P. Dennis,* Sonia Ziesche, and Shanthini Mylvaganam

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.

* 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.

Journal of Bacteriology, September 1998, p. 4804-4813, Vol. 180, No. 18
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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