Fragmentation of 23S rRNA in strains of Proteus and Providencia results from intervening sequences in the rrn (rRNA) genes

Intervening sequences (IVSs) were originally identified in the rrl genes fo r 23S rRNA (rrl genes, for large ribosomal subunit, part of rm operon encod ing rRNA) of Salmonella enterica serovars Typhimurium LT2 and Arizonae, The se sequences are transcribed but later removed during RNase III processing of the rRNA, resulting in fragmentation of the 23S species; IVSs are uncomm on, but have been reported in at least 10 bacterial genera, Through PCR amp lification of IVS-containing regions of the rrl genes we showed that most P roteus and Providencia strains contain IVSs similar to those of serovar Typ himurium in distribution and location in rrl genes. By extraction and North ern blotting of rRNA, we also found that these IVSs result in rRNA fragment ation. We report the first finding of two very different sizes of IVS (113 bp and 183 to 187 bp) in different rrl genes in the same strain, in helix 2 5 of Proteus and Providencia spp.; IVSs from helix 45 are 113 to 123 bp in size, Analysis of IVS sequence and postulated secondary structure reveals s triking similarities of Proteus and Providencia IVSs to those of serovar Ty phimurium, with the stems of the smaller IVSs from helix 25 being similar t o those of Salmonella helix 25 IVSs and with both the stem and the central loop domain of helix 45 IVSs being similar, Thus, IVSs of related sequences are widely distributed throughout the Enterobacteriaceae, in Salmonella, Y ersinia, Proteus, and Providencia spp., but we did not find them in Escheri chia coli, Citrobacter, Enterobacter, Klebsiella, or Morganella spp.; the s poradic distribution of IVSs of related sequence indicates that lateral gen etic transfer has occurred.