UBA6 is an E1 ubiquitin-activating enzyme that initiates ubiquitin conjugation by adenylating ubiquitin's C-terminal glycine and forming a thioester bond with a catalytic cysteine 12. Uniquely among E1 enzymes, UBA6 also activates the ubiquitin-like protein FAT10 through the same mechanism 31. Crystal structures reveal UBA6 undergoes conformational transitions between open (adenylation-competent) and closed (thioester-forming) states, with allosteric regulation by inositol hexakisphosphate 2. UBA6 partners with the dedicated E2 enzyme USE1, distinct from canonical cell cycle E2s 4. In cancer biology, UBA6 is essential for survival of aneuploid epithelial tumors through a complex with BIRC6, KCMF1, and UBR4 that suppresses the integrated stress response 56. Inosine-mediated UBA6 inhibition sensitizes tumors to immune checkpoint blockade by enhancing T cell-mediated cytotoxicity 7. UBA6 also regulates cardiac sodium channel Nav1.5 ubiquitination; elevated UBA6 expression associates with heart failure 8. Disease-associated polyalanine expansion mutations impair UBA6-dependent ubiquitination and E6AP degradation, affecting neuronal survival 9. These findings establish UBA6 as a targetable hub for cancer immunotherapy and a potential therapeutic intervention point in polyalanine expansion diseases.