Figure 1.

The structure of ubiquitin. Ubiquitin is a small, compact protein characterized by a β-grasp fold. The seven lysines that can be linked to the terminal glycine of another ubiquitin molecule to form poly-ubiquitin chains are colored red. The green shading indicates the hydrophobic patch through which ubiquitin interacts with specific ubiquitin-binding proteins.

Image created by Masato Akatsu, Frankfurt University.