Ribosomal RNA processing in saccharomyces cerevisiae

Ribosome biogenesis in eukaryotic cells requires an intricate interplay between a large number of molecules. In the course of this process some 80 ribosomal proteins (r-proteins) have to assemble in an ordered fashion with the four rRNA molecules, which themselves are formed by stepwise maturation of primary transcripts produced by two different RNA polymerases. rRNA processing and r-protein assembly occur concomitantly and are interdependent. Furthermore, a growing number of non-ribosomal components, both proteins and ribonucleoprotein (RNP) particles, is being identified, that are required in trans for the correct and efficient formation of eukaryotic ribosomes. Because of its accessibility to genetic and physiological manipulation, the yeast Saccharomyces cerevisiae has become one of the most popular organisms for studying eukaryotic ribosome biogenesis. In this Chapter we will discuss recent progress in the identification of both cis-acting elements and trans-acting factors involved in the formation of the mature 17S, 26S and 5.8S rRNA species in yeast.