Use of High Resolution Microscopy to Investigate the Functional Role of the Exosome in Sub-Nucleolar Complexes

Abstract

Ribosomal synthesis is a very energy demanding process that initiates with the transcription of precursor ribosomal RNAs (pre-rRNAs) in the nucleolus in eukaryotic cells. RNA polymerase I transcribes the pre-rRNA that contains the sequences of 18S, 5.8S and 25/28S rRNAs, whereas RNA pol III transcribes pre-5S rRNA. These pre-rRNAs undergo many processing reactions that include nucleotide modifications and endo- and exonucleolytic cleavages to give rise to the mature rRNAs, which, together with the approximately 80 ribosomal proteins will form the small and large ribosomal subunits. One of the exonucleases that participate in pre-rRNA processing is the exosome, a complex formed by up to 14 subunits in yeast, responsible for the initial processing of the 7S pre-rRNA to form the mature 5.8S rRNA, and to degrade the 5'-ETS after its release from the primary rRNA transcript.In a recent collaborative work, the yeast exosome localization was studied by our research groups and it was observed that the exosome shows a very peculiar localization within the nucleolus, with an exclusion from a sub-nucleolar compartment enriched in RNA polymerase I. These preliminary results are very intriguing and in order to better understand the functional role of the exosome at these sub-nucleolar compartments, we propose to continue these studies, which may shed more light on the regulation of pre-rRNA processing and quality control, as well as nucleolar partition. This project will also strengthen the collaboration between our groups. (AU)