ATE1 (arginyltransferase 1) catalyzes N-terminal protein arginylation, a post-translational modification that transfers arginine from arginyl-tRNA to aspartate or glutamate residues at protein N-termini 1. This arginylation creates N-degrons that regulate protein degradation through both the ubiquitin-proteasome system and autophagy-lysosome pathways 2. ATE1 contains two adjacent substrate-binding pockets and functions as a homodimer, achieving substrate selectivity through multivalent interactions 2. The human ATE1 gene produces multiple isoforms with distinct structural features and substrate specificities 3, regulated by complex alternative splicing involving competing RNA secondary structures 4. Beyond its canonical degradation function, ATE1 regulates diverse cellular processes including microtubule dynamics via α-tubulin arginylation at E77, which modulates MAP1S binding and microtubule stability 5. Clinically, ATE1 is significantly upregulated in breast cancer, where it promotes progression through MAPK-dependent MYC stabilization and cell proliferation 6. ATE1 also drives melanoma aggressiveness, particularly in NRAS-mutant tumors, and is associated with poor prognosis 7. Cancer-associated non-synonymous SNPs with deleterious consequences on ATE1 structure have been identified 3, suggesting ATE1 as a potential therapeutic target in multiple malignancies.