Our research focuses on how ribosomal subunits are assembled in eukaryotic cells. We use the yeast S. cerevisiae as a model organism to study this essential and highly conserved process. Ribosomes are among of the largest and most complex macromolecular machines assembled in cells. In eukaryotes, the 40S subunit contains a single ribosomal RNA (rRNA) and 32 different ribosomal proteins, while the 60S subunit contains the 3 rRNAs and 47 different ribosomal proteins. Ribosomes are assembled from imported ribosomal proteins on nascent rRNA in the nucleolus of the cell. The large and small subunits are then independently exported through nuclear pores at rates that can reach 30 per second. Both subunits require the export receptor Crm1 for export, and both undergo independent post-export maturation events that are required before the subunits are translation-ready. Over 150 proteins that do not end up as constituents of the mature ribosome are necessary for ribosome biogenesis. The molecular details of how most of these non-ribosomal proteins function is unknown. We have focused our work on the late steps, on export and maturation of the small 40S subunit. In particular, we are characterizing the role of Ltv1, a late adding biogenesis factor that has many characteristics expected of an export-adapter for Crm1, and on RpS3, a ribosomal protein that interacts with Ltv1. We hope to understand better what role ribosomal proteins play in ribosome biogenesis and what role Ltv1 plays in both export and subunit maturation.
