Dihydrouridine synthases are a conserved enzyme family that is encoded by the orthologous COG0042 gene family (Kasprzak et al. 2012 ). Dihydrouridine (D) is a post-trascriptionally modified pyrimidine nucleoside. D results from the reduction of C5,6-double bondof a uridine residue in RNA transcripts (Kasprzak et al. 2012 ) that brings to the addition of two hydrogen atoms C6 and C5. With the absence of the double bond, dihydrouridine is believed to decrease region stability, promoting dynamic motion and accommodating loop structure. D is generated post-transcriptionally by Dus enzymes and it is found in different positions of tRNAs. In s.cerevisiae Dus1 catalyzes the hydrogenation of U17 and U16 in multiple tRNA substrates with flavin mononucleotide (FMN) as a cofactor (Nader et al. 2015 ) to catalyze hybride transfer from NAD(P)H to the uridine substrate (Bishop et al. 2002 ).It is not an essential enzyme.