Recognition and Processing of Misfolded Proteins by PA700, the 19S Regulatory Complex of the 26S Proteasome

The 26S proteasome is composed of the core 20S proteasome in association with the 19S regulatory complex, or PA700. PA700 has multiple activities, including ATPase activity, polyubiquitin-chain binding activity, deubiquitination activity, chaperone-like activity, and substrate remodeling activity. The concerted action of these activities leads to efficient degradation of protein substrates by the 26S proteasome. In this chapter we describe protocols for purifying PA700 and the 20S complexes from bovine red cells and present methods to assay the chaperone-like activity and the substrate remodeling activity of PA700.