Ubiquitination is a post-translational modification of proteins involved in a variety of cellular
processes. Ubiquitination requires the sequential action of three enzymes: E1 (ubiquitin-
activating enzymes), E2 (ubiquitin-conjugating enzymes), and E3 (ubiquitin ligases). This
SnapShot highlights the main types of E3 ubiquitin ligases, which can be classified in three
families depending on the presence of characteristic domains and on the mechanism of
ubiquitin transfer to the substrate protein.