Extended secondary structure as a basis of increased RNA stability in a thermophilic alga Cyanidium caldarium

To identify important structural features in the intergenic sequences of ribosomal DNAs, the nucleotide sequence of the 18-25S rRNA intergenic region was determined in a thermophilic alga, Cyanidium caldarium. Although the mature 5.8S RNA is more stable to thermal denaturation, sequence comparisons reveal a longer molecule with a surprisingly low G/C nucleotide composition. Estimates of the structure further indicate that, unlike other thermophilic examples, thermostability in this organism results, at least in part, from an extended secondary structure.