TRIT1 (tRNA isopentenyltransferase 1) catalyzes the transfer of a dimethylallyl group to adenine at position 37 of both cytosolic and mitochondrial tRNAs, forming N6-(dimethylallyl)adenosine (i6A37) 1. This modification is restricted to specific tRNA substrates including tRNA(Ser) variants and partially the selenocysteine tRNA(Ser)(UCA), making TRIT1 essential for selenoprotein expression 2. TRIT1 contains an amino-terminal mitochondrial targeting sequence enabling dual subcellular localization and substrate specificity primarily determined by tRNA A36-A37-A38 sequence recognition 3. Pathogenic TRIT1 mutations cause combined oxidative phosphorylation deficiency 35, a rare mitochondrial disorder characterized by myoclonic epilepsy, speech delay, strabismus, progressive spasticity, and variable developmental delay 4. Defective tRNA isopentenylation reduces energy metabolism through impaired mitochondrial protein translation 5. Conversely, TRIT1 functions as a candidate tumor suppressor; reduced expression in lung cancer cells restores tumorigenic potential, while restoration suppresses colony formation and xenograft tumor development 6. Recent evidence reveals TRIT1 overexpression correlates with poor hepatocellular carcinoma prognosis and reduced cytotoxic immune infiltration 7, suggesting complex roles in both metabolic disease and cancer biology. The mevalonate pathway generates substrates for TRIT1-dependent selenoprotein modification, linking tRNA modification to ferroptosis resistance in hepatocellular carcinoma 8.