Figure 1.

Overview of the ITS2 (internal transcribed spacer 2) processing and folding in the ribosome biogenesis of the yeast S. cerevisiae. (a) ITS2 location and processing in pre-rRNA from genome to transcriptome. ITS2 and ITS1 are intercalated in the 18S–5.8S–25S tandem arrays, separating the elements of the pre-rRNA. The endonucleolytic cleavage sites are labelled A–E on the pre-rRNA. ITS2 region is highlighted in dark red in each processing state. (b) ITS2 location in the secondary structure of the 5.8S/25S pre-RNA. The ITS2 and 5.8S are displayed in dark red and bright green, respectively; the six typical domains of 25S are labelled I–VI in distinct colors. (c) The three proposed secondary structure models for ITS2. The C₂ cleavage site is highlighted in red in stem III of the ring-pin model. The secondary structure scheme is taken and modified from S. cerevisiae LSU (http://apollo.chemistry.gatech.edu/RibosomeGallery/).