RLIG1 (RNA 5'-phosphate and 3'-OH ligase 1) is the first human RNA ligase identified, catalyzing RNA ligation through a conserved three-step ATP-dependent mechanism 1. The enzyme autoadenylates at an active site lysine residue, transfers the adenylate to 5'-phosphate termini, and facilitates 3'-OH attack to form 3'-5' phosphodiester bonds 2. RLIG1 exhibits selectivity for single-stranded RNA substrates and can ligate tRNA within the anticodon loop 12. RLIG1 plays a critical role in maintaining RNA integrity under oxidative stress by protecting against reactive oxygen species (ROS)-induced RNA damage 13. Transcriptomic analyses of Rlig1 knockout mice revealed significant alterations in global tRNA levels in female brains 2. RLIG1 also participates in herpesviral circRNA biogenesis, with loss-of-function studies demonstrating decreased viral back-splicing 4. Clinically, RLIG1 is upregulated in triple-negative breast cancer (TNBC) tissue, and high expression correlates with reduced overall survival 5. Mechanistically, RLIG1 functions as an oncogene by activating mTORC1 signaling through ERK interaction, promoting cell cycle progression and tumor proliferation 5. RLIG1-deficient cells demonstrate increased sensitivity to oxidative stress and synthetic lethal interactions with specific compounds, positioning RLIG1 as a potential therapeutic target 63.