Fig. 1.

Overview of the 26S proteasome protein degradation pathway. Proteins are tagged multiple times with Ub, leading to the formation of covalently attached poly-Ub chains on the substrate. These tagged substrates are then directed to the 26S proteasome, where they are recognized, deubiquitinated and unfolded by the 19S RP, followed by translocation to the 20S CP where they are degraded into peptides. For each of these stages the biological questions that were addressed using MS techniques are highlighted.