Determination of 5'-triphosphate terminus of 16S ribosomal RNA precursor.

Abstract

THE genes for the 23S and 16S rRNAs are physically linked1. Using the drugs rifampicin and actinomycin D, it has been shown that the 23S and 16S rRNA cistrons are co-transcribed and the promotor is proximal to 16S rRNA cistron2,3. Recent work with an Escherichia coli strain deficient in RNase III has provided further evidence for co-transcription, showing the presence of a long polycistronic RNA which could be cleaved to the immediate precursors of 23S and 16S rRNAs when treated with RNase III in vitro4. We have now studied the transcription of rRNA in E. coli using γ-32P-labelled triphosphates and have shown that the 16S rRNA precursor in our preparation has a 5′-pppA end and that in our system it is neither cleaved nor replaced by 5′-pA as observed by Takanami5. We have not found any detectable 5′-γ-32P-triphosphate end in the 23S rRNA species. This observation further verifies directly that both the 16S and 23S rRNAs belong to one transcriptional unit in the following order: promotor–16S–23S.