Abstract
The RNA exosome is a multisubunit protein complex involved in RNA surveillance of all classes of RNA, and is essential for pre-rRNA processing. The exosome is conserved throughout evolution, present in archaea and eukaryotes from yeast to humans, where it localizes to the nucleus and cytoplasm. The catalytically active subunit Rrp44/Dis3 of the exosome in budding yeast (Saccharomyces cerevisiae) is considered a protein present in these two subcellular compartments, and here we report that it not only localizes mainly to the nucleus, but is concentrated in the nucleolus, where the early pre-rRNA processing reactions take place. Moreover, we show by confocal microscopy analysis that the core exosome subunits Rrp41 and Rrp43 also localize largely to the nucleus and strongly accumulate in the nucleolus. These results shown here shed additional light on the localization of the yeast exosome and have implications regarding the main function of this RNase complex, which seems to be primarily in early pre-rRNA processing and surveillance.
Highlights
The RNA exosome is a protein complex that participates in processing and degradation of all classes of RNA in eukaryotes [1, 2]
Based on software analyses, we identified the presence of three putative nuclear localization signals (NLSs) in the amino acidic sequence of Rrp44, each overlapping one of the functional domains, PinC, CSD2, and S1, respectively (Fig. 1)
It became clear that the exosome is a protein complex conserved throughout evolution, which is present in the nucleus and cytoplasm of eukaryotic cells, where it interacts with many cofactors and participates in different RNA processing and degradation pathways [3, 35, 36]
Summary
The RNA exosome is a protein complex that participates in processing and degradation of all classes of RNA in eukaryotes [1, 2]. Analysis of the subcellular localization by fluorescence microscopy shows that despite being considered a nuclear and cytoplasmic protein [5, 32], full-length GFP-Rrp44 was found mainly concentrated in the nucleus (Fig. 2A), in agreement with high-throughput analyses [24].
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