Ubiquitin conjugating enzyme (Ubc) or E2 enzyme catalyzes the second step in the ubiquitination of a protein tagged to be degraded by the proteasome. Ubiquitin activating enzyme (E1) and ATP produce a C-terminal acyl adenylated ubiquitin molecule which binds to ubiquitin conjugating enzyme (Ubc) cysteine. The Ubc then binds to ubiquitin ligase (E3) via a conserved binding region. E3 catalyzes the transfer of ubiquitin from the Ubc-ubiquitin complex to a lysine residue of the target protein. Ubc13 makes a catalytically active heterodimer with MMS2.
