(NSI News Source Info) May 6, 2009: The exosome complex (or PM/Scl complex, often just called the exosome) is a multi-protein complex capable of degrading various types of RNA (ribonucleic acid) molecules. Exosome complexes can be found in both eukaryotic cells and archaea, while in bacteria a simpler complex called the degradosome carries out similar functions. The core of the complex has a six-membered ring structure, to which other proteins are attached. In eukaryotic cells, the complex is present in the cytoplasm, nucleus and especially the nucleolus, although different proteins interact with the complex in these compartments, in order to regulate the RNA degradation activity of the complex to substrates specific for these cell compartments.
Substrates of the exosome include messenger RNA, ribosomal RNA, and many species of small RNAs. The exosome has an exoribonucleolytic function, meaning it degrades RNA starting at one side (the so-called 3′ end this case), rather than cleaving the RNA at specific sites. Although no causative relation between the complex and any disease is known, several proteins in the complex are the target of autoantibodies in patients with specific autoimmune diseases (especially the PM/Scl overlap syndrome) and some antimetabolitic chemotherapies for cancer function by blocking the activity of the complex.