Figure 1.

Schematic overview of eukaryotic ribosome biogenesis in yeast. The synthesis of ribosomes starts in the nucleolus with the transcription of the 35S pre-rRNA, containing the 18S, 5.8S and 25S rRNAs and co-transcriptional protein assembly to form the small subunit processome. Upon endonucleolytic cleavage within the 35S pre-rRNA, the maturation pathways of the small and the large subunit are separated. The pre-40S subunit (orange) is rapidly exported to the cytoplasm, while the pre-60S subunit (blue) has to undergo numerous rearrangements and processing steps before its nuclear export. In the cytoplasm the last maturation and quality control steps occur before the subunits become competent for joining and translation. The respective (pre-)rRNAs are depicted in blue (rRNAs of the 60S subunit) and orange bars (rRNAs of the 40S subunit), respectively. Dashed arrows symbolize the complex disassembly, recycling and association cycles of assembly factors during ribosome biogenesis.