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Journal of Bacteriology, September 1999, p. 5201-5209, Vol. 181, No. 17
Microbial Collection and Screening
Laboratory, Institute of Molecular and Cell Biology, National
University of Singapore, Singapore 117609
Received 1 February 1999/Accepted 9 May 1999
We describe here the presence of two distinct types of rRNA operons
in the genome of a thermophilic actinomycete Thermomonospora chromogena. The genome of T. chromogena contains six
rRNA operons (rrn), of which four complete and two
incomplete ones were cloned and sequenced. Comparative analysis
revealed that the operon rrnB exhibits high levels of
sequence variations to the other five nearly identical ones throughout
the entire length of the operon. The coding sequences for the 16S and
23S rRNA genes differ by approximately 6 and 10%, respectively,
between the two types of operons. Normal functionality of
rrnB is concluded on the basis of the nonrandom
distribution of nucleotide substitutions, the presence of compensating
nucleotide covariations, the preservation of secondary and tertiary
rRNA structures, and the detection of correctly processed rRNAs in the
cell. Comparative sequence analysis also revealed a close evolutionary
relationship between rrnB operon of T. chromogena and rrnA operon of another thermophilic
actinomycete Thermobispora bispora. We propose that
T. chromogena acquired rrnB operon from
T. bispora or a related organism via horizontal gene transfer.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Distinct Types of rRNA Operons Exist in the Genome
of the Actinomycete Thermomonospora chromogena and Evidence
for Horizontal Transfer of an Entire rRNA Operon
*
Corresponding author. Mailing address: Institute of
Molecular and Cell Biology, National University of Singapore, 30 Medical Dr., Singapore 117609. Phone: 65-7783207. Fax:
65-7791117. E-mail: mcbwangy{at}imcb.nus.edu.sg.
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