Exosome Complex

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 are found in both eukaryotic cells and archaea, while in bacteria a simpler complex called the degradosome carries out similar functions.

The core of the exosome contains a six-membered ring structure to which other proteins are attached. In eukaryotic cells, the exosome complex is present in the cytoplasm, nucleus and especially the nucleolus, although different proteins interact with the exosome complex in these compartments regulating the RNA degradation activity of the complex to substrates specific to 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 end (the 3′ end in this case), and in eukaryotes also an endoribonucleolytic function, meaning it cleaves RNA at sites within the molecule.

Mutations in exosome component 3 cause pontocerebellar hypoplasia and spinal motor neuron disease. In addition, several proteins in the exosome 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 exosome.