Wybutosine (yW) is a hypermodified guanosine at the 3-prime position adjacent to the anticodon of phenylalanine tRNA that stabilizes codon-anticodon interactions during decoding on the ribosome. TYW3 is the human homolog of a yeast gene essential for yW synthesis (Noma and Suzuki, 2006).[supplied by OMIM, Mar 2008].