The eukaryotic RNA exosome is a 9–11-subunit 3′→5′ exoribonuclease complex that catalyses cellular RNA degradation. Liu et al. determined the structure of the reconstituted 9-subunit 286-kDa human exosome at 3.35-Å resolution. The human exosome complex forms a six-membered ring structure, which consists of six different proteins (Rrp41, Rrp45, Rrp46, Rrp43, Mtr3 and Rrp42). The remaining three proteins (Rrp4, Csl4 and Rrp40) form a cap structure that is thought to stabilize the exosome complex. Even though the structure is conserved among bacterial, archaeal and human exosomes, the enzymatic properties vary. Whereas the archaeal exosome has three active sites, the human exosome contains just one, which contains processive phosphorolytic activity provided by the Rrp41–Rrp45 dimer. The processive hydrolytic activity of the ten-subunit yeast exosome is contributed by the yeast-specific subunit Rrp44 (also known as Dis3). The human and yeast nuclear exosomes include a 10th and 11th subunit, respectively, known as Rrp6, which has distributive hydrolytic activity. As the individual catalytic subunits are also active by themselves, the authors suggest that other exosome components might provide regulatory functions.
REFERENCE Liu, Q. et al. Reconstitution, activities, and structure of the eukaryotic RNA exosome. Cell 127 1223–1237 (2006)
This is a preview of subscription content, access via your institution
