Enhances ubiquitin ligase activity of RING-type zinc finger-containing E3 ubiquitin ligases. Proposed to act through recruitment and/or stabilization of the E2 ubiquitin-conjugating enzyme at the E3:substrate complex. MAGEF1-NSMCE1 ubiquitin ligase complex promotes proteasomal degradation of MMS19, a key component of the cytosolic iron-sulfur protein assembly (CIA) machinery. Down-regulation of MMS19 impairs the activity of several DNA repair and metabolism enzymes such as ERCC2/XPD, FANCJ, RTEL1 and POLD1 that require iron-sulfur clusters as cofactors. May negatively regulate genome integrity by inhibiting homologous recombination-mediated double-strand break DNA repair (PubMed:29225034). Interacts (via MAGE domain) with RING-type zinc finger-containing E3 ubiquitin-protein ligases LNX1, TRIM27 and NSMCE1; the interaction is direct. Ubiquitous.