Fig. 1.

Schematic of ribosome biogenesis. a Eukaryotic ribosome biogenesis is a highly orchestrated process involving RNA Pol I, Pol II, and Pol III, which are responsible for transcribing rDNA to rRNA, producing 47S pre-rRNA in the nucleolus. The 4 rRNAs then assemble together with RPs to form a small ribosomal subunit (40S) and a large ribosomal subunit (60S). After assembly, the ribosome complex is exported from the nucleolus to the cytoplasm to form mature ribosomes for protein synthesis. b Bacterial ribosome biogenesis starts with the transcription of the precursors of 23S, 16S, and 5S rRNAs, and some tRNAs in the cytoplasm. The rRNAs then assemble with RPs to form a 30S small subunit and a 50S large subunit. After assembly, the ribosome complex forms mature ribosomes for protein synthesis. RP ribosome protein, RNA pol Ι/II/III RNA polymerase Ι/II/III, RNAP RNA polymerase, rDNA ribosomal DNA, rRNA, ribosomal RNA, tRNA transfer RNA