The methyltransferase TYW3 (tRNA-yW- synthesising protein 3) has been identified in yeast to be involved in wybutosine (yW) biosynthesis [1]. yW is a complexly modified guanosine residue that contains a tricyclic base and is found at the 3' position adjacent the anticodon of phenylalanine tRNA. TYW3 is an N-4 methylase that methylates yW-86 to yield yW-72 in an Ado-Met-dependent manner [1].

1: Biosynthesis of wybutosine, a hyper-modified nucleoside in eukaryotic phenylalanine tRNA. Noma A, Kirino Y, Ikeuchi Y, Suzuki T; EMBO J. 2006; [Epub ahead of print] PMID:16642040