Putative promoter elements for the ribosomal RNA genes of the thermoacidophilic archaebacterium Sulfolobus sp. strain B12.

In Sulfolobus sp. strain B12, single-copy genes encode the three ribosomal RNAs. The genes for the 16S rRNA and for the 23S rRNA are closely linked but separated from the 5S rRNA gene. Transcription of the 16S/23S rRNA gene cluster starts 139 nucleotides upstream of the 5'-end of mature 16S rRNA. For the 5S rRNA gene the point of transcription initiation coincides with the 5'-end of mature 5S rRNA. The comparison of the upstream regions for these transcriptional start sites shows the presence of a completely conserved trinucleotide sequence around the point of transcription initiation and a completely conserved octanucleotide sequence about 22 nucleotides upstream of it. These sequences are only moderately homologous to putative promoter elements for stable RNA genes in the closely related archaebacterium Thermoproteus tenax (1), but they are very similar to corresponding sequences in the distantly related archaebacterium Methanococcus vannielii (2). The consensus sequence found for Sulfolobus and Methanococcus could therefore constitute the archetype of an archaebacterial promoter for stable RNA genes.