Ubiquitin-conjugating enzyme E2 variant 2 (MMS2) catalyzes the synthesis of non-canonical poly-ubiquitin chains that are linked through 'Lys-63'Ia a heterodimer that This type of poly-ubiquitination does not lead to protein degradation by the proteasome. MMS2 has no ubiquitin ligase activity on its own. MMS2 mediates transcriptional activation of target genes and plays a role in the control of progress through the cell cycle and differentiation. MMS2 plays a role in the error-free DNA repair pathway and contributes to the survival of cells after DNA damage.