CTPS1 (CTP synthase 1) is a crucial enzyme that catalyzes the de novo synthesis of cytidine triphosphate (CTP), a precursor essential for DNA, RNA, and phospholipid biosynthesis 1. The enzyme converts UTP to CTP through ATP-dependent amination using glutamine or ammonia as nitrogen sources 1. CTPS1 plays a particularly important role in immune cell proliferation, as activated lymphocytes require increased CTP for enhanced DNA, RNA, and membrane synthesis 2. Beyond its metabolic function, CTPS1 exhibits protein deamidase activity that regulates immune responses and DNA repair. Specifically, CTPS1 deamidates asparagine-85 of IRF3, preventing its DNA binding and suppressing interferon induction, thereby negatively regulating innate immunity 3. Additionally, CTPS1 facilitates chr1 relaxation during DNA repair by deamidating histones H1 at asparagines-76 and -77, promoting subsequent acetylation and increasing chr1 accessibility for DNA repair proteins 4. Clinically, CTPS1 deficiency causes immunodeficiency-24, characterized by impaired T and B cell expansion 2. CTPS1 is also implicated in cancer progression and drug resistance, making it a potential therapeutic target in multiple myeloma, colorectal cancer, and other malignancies 15.