The mammalian ribosome is composed of 4 RNA species and approximately 80 different ribsomal proteins (RPs).

In the eukaryotic ribosomal RNA processing pathway, a complex of ten riboexonucleases called the exosome that plays a central role in the precise formation of the 3' ends of several types of RNAs.

The exosome also destroys excess ribosomal RNA precursors and unused intermediates and degrades poly(A)-mRNAs in the cytoplasm.

In the nucleus, the complex appears to function in a regulated mRNA surveillance system that degrades transcripts in response to defects in the mRNA processing and export pathways.

References

 Moss T. At the crossroads of growth control; making ribosomal RNA. Curr Opin Genet Dev. 2004 Apr;14(2):210-7. PMID: #15196469#

 Butler JS. The yin and yang of the exosome. Trends Cell Biol. 2002 Feb;12(2):90-6. PMID: #11849973#