Figure 1.

Schematic representation of ATP-powered proteolysis in the cytosol of plant cells. Proteins are tagged with multi-ubiquitin chains by the action of a series of ubiquitin ligases (E1, E2, and E3) and are targeted for degradation by the 26S proteasome. The 26S proteasome consists of the 20S proteasome sandwiched between two 19S regulatory particles. Upon binding of the protein substrate to the 26S proteasome, ubiquitin chains are recycled, and the protein is unfolded and degraded to oligopeptide fragments. E1: ubiquitin-ligase enzyme; E2: ubiquitin-conjugating enzyme; E3: ubiquitin-ligating enzyme.