Exosome Component

EXOSC9 is a non-catalytic component of the RNA exosome complex which has 3'->5' exoribonuclease activity and take part in many cellular RNA processing and degradation events. In the nucleus, the RNA exosome complex take part in proper maturation of stable RNA species like rRNA, snRNA and snoRNA, in the elimination of RNA processing by-products and non-coding 'pervasive' transcripts like anti-sense RNA species and promoter-upstream transcripts (PROMPTs), and of mRNAs with processing defects, thereby limiting or excluding their export to the cytoplasm. The RNA exosome is involved in Ig class switch recombination (CSR) and/or Ig variable region somatic hypermutation (SHM) by targeting AICDA deamination activity to transcribed dsDNA substrates. In the cytoplasm, the RNA exosome complex takes part in general mRNA turnover and specifically degrades inherently unstable mRNAs containing AU-rich elements (AREs) within their 3' untranslated regions, and in RNA surveillance pathways, inhibiting translation of aberrant mRNAs. EXOSC9 takes part in degradation of histone mRNA. The catalytic inactive RNA exosome core complex of 9 subunits (Exo-9) is proposed to be an essential part in the binding and presentation of RNA for ribonucleolysis, and acts as a scaffold for the association with catalytic subunits and accessory proteins or complexes. EXOSC9 binds to ARE-containing RNAs.

Exosome component 8 and transcription factor 4 (EXOSC8) is a part of the exosome complex. In the cytoplasm, the RNA exosome complex is engaged in general mRNA turnover and specifically degrades naturally unstable mRNAs containing AU-rich elements (AREs) within their 3' untranslated regions, and in RNA inspection pathways, preventing translation of aberrant mRNAs. EXOSC8 appears to be involved in degradation of histone mRNA. EXOSC8 attaches to ARE-containing RNAs. The EXOSC8 gene encodes a 3'-5' exoribonuclease, which specifically interacts with mRNAs containing AU-rich elements. The EXOSC8 protein is part of the exosome complex, which is significant for the degradation of many RNA species.

EXOSC7, a component of the RNA exosome complex, is a member of the RNase PH family. EXOSC7 takes part is several pathways such as transfer to a nascent protein and Unfolded Protein Response and Biosynthesis of the N-glycan precursor (dolichol lipid-linked oligosaccharide, LLO). A significant paralog of this gene is EXOSC9.

EXOSC5 is a member of the RNase PH family. EXOSC5 is known to cooperate with Exosome component 8 and Exosome component 1. EXOSC5 is a Non-catalytic component of the RNA exosome complex and has 3'->5' exoribonuclease activity. EXOSC5 take part in a large number of cellular RNA processing and degradation events. EXOSC5 is expressed in a large range of hematopoietic and epithelial tumor cell lines, but not in standard hematopoietic tissues or other standard tissue, with the exception of testis.

Exosome Component 3 (EXOSC3) is a non-catalytic component of the human exosome, a complex with 3'-5' exoribonuclease activity. EXOSC3 takes part in various RNA processing and degradation activities including degradation of histone mRNA. Linked pseudogenes of EXOSC3 are located on chromosome 19 and 21.

EXOSC10 is a nucleolar protein and represents one crucial component of the so-called "PM/Scl complex" or "nuclear exosome", which is an RNA-processing complex consisting of a number of exoribonucleases (not to be confused with certain multivesicular bodies which are shed by cultured cells into the culture fluid and are also called exosomes).
Autoantibodies against EXOSC10 occur in patients suffering from polymyositis, scleroderma or polymyositis/scleroderma overlap syndromes. While antibodies to other components of the exosome complex (PM/Scl 75, several Rrp proteins) can be found in some sera, practically all patients with autoantibodies against the PM/Scl complex are positive for EXOSC10 antibodies, making this specificity an important marker. The presence of EXOSC10 autoantibodies is a comparatively "good" prognostic sign in polymyositis/scleroderma overlap syndrome unlike the poor prognosis seen when other myositis and systemic sclerosis specific autoantibodies are present.

EXOSC1 is a non-catalytic component of the exosome which has 3'->5' exoribonuclease activity and participates in many cellular RNA processing and degradation occasions. EXOSC1 associates with the exosome by protein-protein interactions with ribosomal RNA-processing protein 42 and ribosomal RNA-processing protein 46.