Structure of mottse rRNA precursors.Complete sequence and potential folding of the spacer regions between 18S and 28S rRNA

Abstract
We have determined the complete nucleotide sequence of the regions of mouse ribosomal RNA transcription unit which seperate mature rRNA genes. These internal transcribed spacers (ITS) are excised from rRNA precursor during ribosome biosynthesis. ITS 1, between 18s and 5.8s rRNA genes, is 999 nucleotides long. ITS 2, between 5.8s and 28s rRNA gnes, is 1089 nucleotides long. Both spacers are very rich in G + C,70 and 74 respectively. Mouse sequences have been compared with the other available eukaryotes : while no homology is apparent with yeast or xenopus, mouse and rat ITS sequences have been largely conserved, with homologous segmaents interspersed with highly divergent tracts. Homology with rat is much more extensive for ITS 1 than for ITS 2. Tentative secondary structure models are proposed for the folding of these regions within rRNA precursor;they are closely related in mouse and rat.