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Journal of Bacteriology, September 2000, p. 4719-4729, Vol. 182, No. 17
Institut für Mikro- und
Molekularbiologie der Justus-Liebig-Universität Giessen,
35392 Giessen, Germany
Received 22 February 2000/Accepted 7 June 2000
We provide experimental evidence for RNase III-dependent
processing in helix 9 of the 23S rRNA as a general feature of many species in the alpha subclass of Proteobacteria
(alpha-Proteobacteria). We investigated 12 Rhodobacter, Rhizobium,
Sinorhizobium, Rhodopseudomonas, and
Bartonella strains. The processed region is characterized by the presence of intervening sequences (IVSs). The 23S rDNA sequences
between positions 109 and 205 (Escherichia coli numbering) were determined, and potential secondary structures are proposed. Comparison of the IVSs indicates very different evolutionary rates in
some phylogenetic branches, lateral genetic transfer, and evolution by
insertion and/or deletion. We show that the IVS processing in
Rhodobacter capsulatus in vivo is RNase III-dependent
and that RNase III cleaves additional sites in vitro. While all
IVS-containing transcripts tested are processed in vitro by RNase
III from R. capsulatus, E. coli RNase
III recognizes only some of them as substrates and in these substrates
frequently cleaves at different scissile bonds. These results
demonstrate the different substrate specificities of the two enzymes.
Although RNase III plays an important role in the rRNA,
mRNA, and bacteriophage RNA maturation, its substrate specificity
is still not well understood. Comparison of the IVSs of helix 9 does
not hint at sequence motives involved in recognition but reveals that
the "antideterminant" model, which represents the most recent
attempt to explain the E. coli RNase III specificity in
vitro, cannot be applied to substrates derived from
alpha-Proteobacteria.
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
RNase III Processing of Intervening Sequences Found in Helix 9 of
23S rRNA in the Alpha Subclass of Proteobacteria
*
Corresponding author. Mailing address: Institut
für Mikro- und Molekularbiologie der
Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 26, 35392 Giessen, Germany. Phone: 49-641-99-35550/57. Fax: 49-641-99-35549. E-mail:
Elena.Evguenieva-Hackenberg{at}mikro.bio.uni-giessen.de.
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