Group-specific differences in the secondary structure of the 28S ribosomal RNA of yeasts.

Ribosomal RNA (rRNA) sequences represent a good taxonomic character. Even small but significant parts of rRNA molecules can be used as a basis for taxonomic conclusions. A highly variable region within the 28S ribosomal nucleotide sequences from various yeasts was analysed. Despite numerous nucleotide exchanges in this region the secondary structure is generally conserved as in helices 17.1 and 17.2. However, among the organisms analysed the basidiomycetous yeasts show an insertion of 30 nucleotides which is missing in other yeasts. In this feature the Taphrinales and Schizosaccharomycetaceae resemble the 28S rRNA of Saccharomyces carlsbergensis rather than that of the basidiomycetous yeasts. Optimal sequence alignment and a good understanding of the secondary structure is an indispensible prerequisite for any evaluation of the taxonomic significance of differences in ribosomal RNA nucleotide sequences.