Transcriptional analysis of Bacillus subtilis rRNA-tRNA operons. II. Unique properties of an operon containing a minor 5 S rRNA gene.

This is part of a series of two papers on gene regulation in Bacillus subtilis rRNA-tRNA operons that contain large clusters of tRNA genes. The preceding paper (Vold, B.S., Okamoto, K., Murphy, B.J., and Green, C.J. (1988) J. Biol. Chem. 263, 14480-14484) investigates the rrnB operon containing 21 tRNA genes, and this paper investigates a B. subtilis rRNA-tRNA operon containing 16 tRNA genes and a minor 5 S rRNA. Hybridization studies suggest this minor 5 S rRNA occurs as a single copy in the B. subtilis 168 genome. S1 nuclease mapping indicates that this minor 5 S rRNA gene has its own promoter. No promoters have been found immediately 5' to any of the major 5 S rRNA species in B. subtilis rRNA operons. S1 mapping of the spacer region between the 23 S and minor 5 S rRNA revealed that the maturation of the 23 S rRNA in this operon may arise from an unusual processing mechanism. S1 nuclease mapping experiments suggest the existence of a promoter element immediately upstream of the last gene, for tRNA(Leu CAA), in the operon. A precursor leucine tRNA resulting from transcription of this last tRNA gene was observed in Northern hybridizations, and the amounts of this precursor increased during sporulation. A single terminator-like element is located just upstream of this last tRNA gene; however, S1 nuclease mapping experiments suggest that some read-through transcription occurs. Thus, all 16 tRNA genes are under control of the upstream 16 S rRNA promoters and the minor 5 S rRNA promoter. However, the last tRNA gene is primarily under the control of its own unique promoter.