tRNAArg-derived fragments mediate protein arginylation [tRNA]

Arginyltransferase ATE1 mediates posttranslational arginylation that plays key roles in mammalian embryogenesis, cell migration, and normal brain function. The molecular mechanisms of arginylation remain elusive. ATE1 utilizes arginyl-tRNAArg as the donor of Arg, putting this reaction into a direct competition with the protein synthesis machinery. Here, we addressed these questions of ATE1- arginyl-tRNAArg specificity as a potential mechanism enabling this competition in vivo. Using in vitro arginylation assays and ATE1 knockout models, we find that while arginylation is specific to tRNAArg, it is able to utilize short tRNAArg derivatives that bear structural resemblance to tRNA-derived fragments (tRF), a new class of small regulatory non-coding RNAs with poorly characterized but critical functions in vivo. Arginyl-tRFArg can be generated in vitro directly from pre-charged -tRNAArg, and ATE1 is able to utilize these arginyl-tRFArg fragments with similar efficiency as arginyl-tRNAArg. Lack of arginylation in ATE1 knockout cells leads to a decrease in tRFArg generation and a significant increase in the ratio of tRNAArg to tRFArg compared to wild type, suggesting a functional link between tRFArg and arginylation in vivo. We propose that generation of physiologically important tRFs can play a critical role as a switch between protein translation and arginylation in vivo. Overall design: Comparison between wild-type and Ate1-knockout cells