Maturation of pre‐40S particles in yeast and humans
Résumé
The synthesis of ribosomal subunits in eukaryotes requires the interplay of numerous maturation and assembly factors (AFs) that intervene in the insertion of ribo-somal proteins within pre-ribosomal particles, the ribosomal subunit precursors, aswell as in pre-ribosomal RNA (rRNA) processing and folding. Here, we review theintricate nuclear and cytoplasmic maturation steps of pre-40S particles, the precur-sors to the small ribosomal subunits, in both yeast and human cells, with particularemphasis on the timing and mechanisms of AF association with and dissociationfrom pre-40S particles and the roles of these AFs in the maturation process. Wehighlight the particularly complex pre-rRNA processing pathway in human cells,compared to yeast, to generate the mature 18S rRNA. We discuss the informationgained from the recently published cryo-electron microscopy atomic models ofyeast and human pre-40S particles, as well as the checkpoint/quality control sys-tems that seem to operate to probe functional sites within yeast cytoplasmic pre-40S particles.