Exosome is a multiprotein complex responsible for processing and degradation of many types of RNAs in eukaryotic cells. This complex localizes both to the nucleus and cytoplasm. The exosome complex has two catalytic subunits: Rrp6, found only in the nucleus, and Rrp44, found in the nucleus and in the cytoplasm of Saccharomyces cerevisiae. The Rrp44 is an essential protein of the RNase II class, which has endonucleolytic and exonucleolytic activities. Due to the importance of the exosome for the posttranscriptional control of gene expression both in the nucleus and in the cytoplasm, our laboratory has started a study on the cellular transport of the exosome subunit Rrp6, which resulted in a recent publication on the identification of the karyopherins involved in the nuclear import of this exosome subunit. Despite this initial information, little is known about the mechanism responsible for the transport of other exosome subunits. To continue that work, nuclear localization signals (NLS) were identified in the Rrp44 subunit sequence, suggesting that this protein may also be transported to the nucleus independently of the exosome complex. This project aims at the identification of the pathways involved in the nuclear transport of Rrp44, as well as of other exosome subunits.
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