Figure 1. Overview of eukaryotic ribosome biogenesis.

In the nucleolus, a rRNA precursor is transcribed by RNAPI and co‐transcriptionally joined by RPs and RBFs, giving rise to a 90S pre‐ribosomal particle. After pre‐rRNA cleavage (site 2 in human, A₂ in yeast), the pre‐40S and pre‐60S particles further mature independently in the nucleolus and the nucleoplasm. After export through the nuclear pore complex, final maturation steps occur in the cytoplasm, yielding 40S and 60S subunits competent for mRNA translation. RNAPIII transcribes the 5S rRNA (nucleolar in human cells, nucleoplasmic in yeast), which joins pre‐60S particles in the nucleolus as part of the 5S RNP complex. RNAPII transcribes mRNAs of RP and RBF genes, which are translated by the 80S ribosome in the cytoplasm and then imported into the nucleus. Structural snapshots of maturing 90S (PDB ID: 6ZQA, 6ZQC), pre‐40S (PDB ID: 6G4W, 6G4S, 6ZQF), and pre‐60S particles (PDB ID: 6EM3, 6C0F, 6ELZ, 3JCT, 5JCS, 6LU8, 6LSR) as well as mature subunits (PDB ID: 6G5H, 3J7P) are shown. RBFs are displayed in orange, Rps in green, Rpl in blue, rRNA in gray. Structures solved in yeast are shown with reduced opacity, currently no structures of the corresponding human maturation stages are available.