Mms2 is a UEV (ubiquitin E2 variant) protein that acts with the E2 enzyme Ubc13 in a heterodimeric complex which assembles K63-linked polyubiquitin chains utilized in non-degradative ubiquitin signaling pathways (DNA repair, signal transduction). The UEV proteins are structurally similar to E2 enzymes displaying the same fold, but lacking the active site cysteine of the E2. The Ubc13/Mms2 complex is unique in that it is has the ability to form free K63-linked polyubiquitin chains in solution in the absence of an E3.
