Post-transcriptional modifications in ribosomal RNA are believed to fine-tune the RNA functions. The present study describes the characterization of the post-transcriptional modifications in Clostridium acetobutylicum 16S rRNA,
using high-pressure liquid chromatography (HPLC) coupled to electrospray ionization mass spectrometry and reverse transcriptase assays. The combination of these techniques allowed the identification of eleven modified nucleosides,
which were mapped onto the rRNA sequence. The C. acetobutylicum modification map is similar to that of Escherichia coli, with the majority of the modifications near functionally important sites in the rRNA. Although, in general, the number of modifications in rRNA is smaller than in tRNA, the conservation of the modification sites seems to
indicate that the post-transcriptional modifications in 16S rRNA provide a necessary prerequisite for the ribosomal function.