Ribosomes: An Exciting Avenue in Stem Cell Research

Figure 1

Eukaryotic ribosome synthesis. Eukaryotic ribosome synthesis is a complex process that comprises 5 steps, including transcription, processing, modification, assembly, and transport. (1) Transcription: RNA polymerase I transcribes rDNA into 47S preRNA. RNA polymerase III transcribes 5S rRNA. snoRNAs are transcribed by RNA polymerase II or III from non-protein-encoding regions or mRNA introns. RNA polymerase II transcribes the mRNAs for ribosome proteins (RPs) and assembly factors (AFs). (2) Processing: 47S pre-rRNA is processed to 18S, 28S, and 5.8S rRNAs. (3) Modification: there are two primary kinds of modifications on rRNA that are mediated by snoRNAs: 2-O-methylation (2-O-Me) and pseudouridines (Ψ). (4) Assembly: RPs and AFs are translated in the cytoplasm and shuttled to the nueclus for ribosome assembly. The pre-60S subunits comprise 28S, 5.8S, and 5S rRNA, and the pre-40S subunit includes an additional 18S rRNA. (5) Transport: the subunits are transported to the cytoplasm via the nuclear pore to be assembled as needed during translation.