In recent years, it has become clear that RNAs play an even more significant role within cells than previously thought; they are not only the conveyer of genetic information, but can themselves be regulators of gene expression. All of these RNA species share the fact that, after transcription, they assemble into ribonucleoprotein (RNP) complexes to get modified, processed and transported to their final destination within the cell. However, for each of these RNA species, this maturation occurs by a different pathway defined by very specific processing factors. These factors form discrete subsets of proteins that associate with each species of RNA in a dynamic fashion to define the order of maturation events. The coordination of processing and assembly events but also the spatiotemporal dynamics of the steps involved is still not well understood.
Ribosomes are the protein translation machinery and therefore essential to every cell. In this role, they have a profound effect on the correct function and growth of a cell, and incorrect modification, processing and assembly has been linked to defects in growth and division in yeast cells, but also to specific diseases in humans and mice. Ribosome biogenesis involves ~200 proteins to process only three different RNAs, due to the enormous complexity of correct pre-rRNA processing and assembly. This entails concurrent assembly of ribosomal proteins, correct timing of processing steps with structural rearrangements. The association of different factors is believed to facilitate all these steps and ensure the exact timing of events. Despite the identification of a large number of proteins involved in ribosome maturation and their associated complexes, the larger, dynamic picture of ribosome assembly still remains unclear, as these complexes represent only a static picture of one or a population of sub-complexes.