LIG_Rrp6Rrp47_Mtr4_1

The core function of the exosome complex is to cleave RNA molecules. This can either be for RNA processing or RNA destruction purposes. The function of any given exosome complex is individually purposed by the binding of additional proteins and protein complexes: The system is modular. Through the interaction of the Rrp6-Rrp47-Mtr4 complex (Q12149; P38801; P47047) plus Mpp6 (P53725) with exosome complexes, the RNA-processing ability of the nuclear exosome is broadened. Nuclear transcription generates large precursor molecules prior to the mature RNAs. For rRNA, snRNA, and snoRNA maturation, the 3’-end of the precursor molecule needs to be shortened. This process is mainly driven by the exosome itself, a complex of ribonucleases which is also involved in RNA turnover and surveillance of tRNA and mRNA precursors in the nucleus. To ensure that Mtr4 is only able to bind to the exosome within the nucleus, it needs to interact with the heterodimer of two additional nuclear proteins Rrp6 and Rrp47 before being able to attach to the exosome complex (4WFD). In the exosome complex, Mtr4 works as a helicase by unwinding double-stranded segments of the RNA whereas Rrp6 works as an exoribonuclease within the exosome (Schuch,2014). The Rrp6/Rrp47-binding motif appears to be unique to Mtr4. Mtr4 has both Rrp6-dependent and independent functions. It is also a part of the TRAMP complex involved in RNA polyadenylation as well as degradation (Mitchell,2014). The RNA-degrading exosome complex should not be confused with the extracellular vesicles also known as exosomes.