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. Author manuscript; available in PMC: 2017 Mar 1.
Published in final edited form as: Prog Retin Eye Res. 2015 Sep 4;51:69–89. doi: 10.1016/j.preteyeres.2015.09.002

Figure 11. Ubiquitin conjugation marks proteins for proteasome degradation.

Figure 11

The coordinate action of the enzymes E1, E2, and E3 actively conjugate ubiquitin proteins to a lysine (K) residue on the protein substrate to mark it for proteasome degradation. An ubiquitin chain of at least 4 proteins is required for recognition by the regulatory complex of the 26S proteasome. Following binding of the Ub-protein, the regulatory complex deubiquitinates the substrate prior to protein unfolding and translocation into the core, where it is degraded to small peptides. The ubiquitin is recycled for another round of protein marking.