Nucleotide sequence of the 18-25 S ribosomal RNA intergenic region from a thermophile, Thermomyces lanuginosus.

To identify important structural features in the intergenic sequences of ribosomal DNAs, the nucleotide sequence of the 18-25 S rRNA intergene region was determined in a thermophilic fungus, Thermomyces lanuginosus, and compared to that of common yeasts. While a striking sequence homology was observed in the mature ribosomal sequences, the two internal transcribed spacer regions were found to be unusually G + C rich and significantly shorter than any other organism. An extensive secondary structure could be predicted but estimates of the secondary structure did not reveal a minimum structure which is common to other species; rather, in all rDNA transcripts the intergenic regions appear organized into a secondary structure in which all of the mature rRNA junctions are localized within one domain. This suggests that a role of the internal transcribed spacer in ribosome maturation may be that of a "biological spring" which maintains processed sites in close proximity.