Characterization of the three ribosomal RNA operons rrnA, rrnB, and rrnC, from Brucella melitensis

The three Brucella melitensis ribosomal RNA operons rrnA, rrnB, and rrnC we re characterized individually. Each locus consisted of the 16S rRNA gene (r rs), followed by an intergenic spacer containing the tRNA-Ile and tRNA-Ala genes, the 23S rRNA gene (rrl), an intergenic spacer devoid of tRNA genes, the 5S rRNA gene (rrf), and an f-Met tRNA gene. The DNA sequences were iden tical over a 6271 bp region, diverging 594 bp upstream of rrs and immediate ly downstream of the f-Met tRNA gene. The previously uncharacterized 23S rR NA genes each contained a 178 bp insertion 130 bp from the 5' end. The loca tion of the insertion matched intervening sequences (IVSs) found in other R hizobiaceae. However, the size and sequence of the Brucella IVS differed fr om all previously reported IVS sequences from bacteria. The IVS region was PCR-amplified from 20 Brucella isolates representing all known Brucella spe cies and biovars. All isolates contained only the complete IVS fragment. We compared the IVS DNA sequences of rr IC from representative strains of eac h of the six known Brucella species. The data revealed that the sequences w ere identical and differed from the B. melitensis IVS sequences by a single base pair. In other bacterial species, the IVSs are associated with post-t ranscriptional processing of the 23S rRNA by RNase III. We found that the B rucella 23S rRNA was slightly smaller than the 23S rRNA of Escherichia coli , known to be devoid of IVS sequences. (C) 2000 Elsevier Science B.V. All r ights reserved.