The process begins with the activation of ubiquitin by the enzyme E1 ubiquitin-activating enzyme. This activated ubiquitin is then transferred to a E2 ubiquitin-conjugating enzyme. An E3 ubiquitin ligase finally facilitates the transfer of ubiquitin from the E2 enzyme to the target protein. Polyubiquitination signals the protein for degradation by the proteasome, where it is broken down into peptides and amino acids.
