The exosome is a multiprotein complex involved in the processing of almost every RNA in the cell. Exosome main functions include non-coding RNA degradation, mRNA turnover and ribosomal RNA maturation. In Saccharomyces cerevisiae cells, the exosome is present in both the nucleus and the cytoplasm, but the composition of the complex varies depending on the cellular location. The nuclear exosome comprises 11 subunits, two of them are catalytically active, Rrp44 and Rrp6, while the cytoplasmic exosome lacks Rrp6. Even though the nuclear and cytoplasmic exosomes have similar compositions, it is unknown whether the exosome is transported to the nucleus as a previously assembled complex, or whether the different subunits are transported individually. Although the exosome structure and function has been subject to many studies in the last years, information on the nuclear transport pathway of this complex is lacking. Because the main function of the nuclear exosome is in the maturation of pre-rRNAs, it is of great interest to uncover how the exosome is transported from the cytoplasm to the nucleus and understand how this complex is assembled. To better understand the nuclear import of the exosome, our research group is studying the transport of the catalytic subunit Rrp44 by using fluorescence and confocal microscopy. In order to confirm the results we have obtained during the first year of this project, studies using the photobleaching microscopy and Spinning Disk confocal microscopy techniques are necessary. Furthermore, a better nucleolar protein marker and a better resolution of the images would allow us to confirm our results. Professor Olivier Gadal is a reference in the field of yeast ribosomal transport by using high resolution microscopy. We believe that experiments carried out in Doctor Gadal's lab will help us elucidate exosome biogenesis and better understand the function of this important complex in the cell.
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