Mammalian Trit1 is a tRNA[Ser]Sec-isopentenyl transferase required for full selenoprotein expression

Selenoproteins are proteins carrying the rare amino acid Sec (selenocysteine). Full expression of selenoproteins requires modification of tRNA([Ser]Sec), including N-6-isopentenylation of base A(37). We show that Trit1 is a dimethylallyl:tRNA([Ser]Sec) transferase. Knockdown of Trit1 reduces expression of selenoproteins. Incubation of in vitro transcribed tRNA([Ser]Sec) with recombinant Trit1 transfers [C-14]dimethylallyl pyrophosphate to tRNA([Ser]Sec). 37A>G tRNA([Ser]Sec) is resistant to isopentenylation by Trit1.