Exosome complex

The exosome (also PM / Scl complex) is a protein complex that plays a role in the degradation of ribonucleic acids (RNA). At the core of the exosome are among other six characteristically arranged in a ring proteins. The exosome is in living nature a very widespread and evolutionarily old protein complex. It occurs in both archaea as well as in the cells of eukaryotes. In eukaryotic cells, the protein complex can be found in both the cytoplasm and the nucleus, and is essential for the growth of these cells. In bacteria, its function is taken over by the Degradosom.

Construction

The core of the exosome of eukaryotes and archaea is, as well as the structurally related polynucleotide phosphorylases ( PNPasen ) of Degradosoms of bacteria arranged in a ring of six core proteins, three Cap proteins and a central pore. Often these core occur forming proteins in complex with additional proteins.

All six core proteins are ribonucleases ( RNases ) of ribonuclease PH family. While the core of the exosome of archaea from only two different ribonucleases (three molecules Rrp41 and Rrp42 ) is the core of the exosome of eukaryotes by means of six different ribonucleases ( Rrp41, Rrp45, Rrp42, Rrp43, Mtr3 and Rrp46 ) is established. The eukaryotic proteins Rrp41, Rrp46 Mtr3 and Rrp41 in the archaea and the eukaryotic proteins Rrp45, Rrp42 and Rrp43 in Rrp42 the archaea find their respective equivalent.

The lying directly on the six core ribonucleases Cap proteins possess an S1 RNA - binding domain. In archaea, the Cap proteins by two molecules Rrp4 and a molecule CSL4 are represented. The Cap proteins of eukaryotes consist of three different molecules ( Rrp4, Rrp40 and CSL4 ). Both Rrp4 and Rrp40 of eukaryotes correspond to the Rrp4 the archaea.

The most common two eukaryotic proteins, the core and cap proteins occur in solid company forming the core are Rrp44 and Rrp6. While Rrp44 is a ribonuclease of the RNase R family, Rrp6 belongs to Ribonukleasenfamilie D. In addition, the components of the exosome protein complex with numerous regulatory proteins interact.

Function

The exosome is an involved in the cleavage of ribonucleic enzyme complex. Depending on the cell compartment and, depending on the regulatory proteins involved be implemented as a substrate messenger RNA (mRNA ), ribosomal RNA (rRNA ) or small RNAs. In the cytosol, the exosome is particularly involved in the degradation of messenger RNA. The enzyme complex occurs, inter alia, proteins which recognize specific patterns ( so-called AU-rich elements ) in the 3'- untranslated region of the messenger RNA, in combination. In the nucleus of the exosome - protein complex for the correct processing of small RNAs is required. In the nucleolus, the nucleus area with the highest Exosomendichte, the enzyme complex in the processing of ribosomal RNA plays a central role beyond.

The functions of the exosome complex enzyme based on its ribonuclease activity. The exosome has Exoribonukleasefunktion, whereby the substrate on the 3 'end of a Ribonukleinsäurestrangs can be reduced. In contrast to the archaea exosome the exosome of eukaryotes has an additional Endoribonukleasefunktion which allows a split within a Ribonukleinsäurestrangs. While Exoribonukleasefunktion the exosome of archaea is taken over by the annularly arranged core proteins and Rrp41 Rrp42, the exosome -associated proteins Rrp6 Rrp44 and are responsible for the function of the RNA-cleaving exosome of eukaryotes.

Although eukaryotes have additional RNA - degrading enzymes, the exosome is essential for cell survival. Experimental inhibition of exosome function, for example with the aid of the RNA interference results in a stop of cell growth or cell death.