tRNA wybutosine-synthesizing protein 5, also known as TYW5, acts as a component of the wybutosine biosynthesis pathway. Wybutosine is a hyper modified guanosine with a tricyclic base found at the 3'-position adjacent to the anticodon of eukaryotic phenylalanine tRNA. TYW5 catalyzes the hydroxylation of 7-(a-amino-a-carboxypropyl)wyosine (yW-72) into undermodified hydroxywybutosine (OHyW). OHyW is a derivative of wybutosine found in higher eukaryotes. Recombinant human TYW5 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.