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. Author manuscript; available in PMC: 2014 Mar 1.
Published in final edited form as: Crit Rev Biochem Mol Biol. 2012 Dec 13;48(2):89–97. doi: 10.3109/10409238.2012.742856

Figure 1.

Figure 1

Overview of the Ubiquitin-Proteasome System (UPS). Two steps are involved. The first step is the ubiquitination. In this step, three enzymes: activating enzyme E1, conjugating enzyme E2 and E3 ubiquitin ligase. Ubiquitin first forms a covalent bond with E1, then transferred to E2. Then ubiquitin and E2 forms a complex with substrate and E3 to help ubiquitin trasfer to substrate. This process repeats until substrate is labeled by a chain of ubiquitins. The second step is the degradation. The ubiquitin labeled substrate is released from the E3 ubiquitin ligase. It is recognized and deubiquinated by proteasome. The substrate is degraded.