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-transcriptionally modified pyrimidine nucleoside. D results from the reduction of C5,6-double bond of 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 E.coli, tRNA-dihydro uridine (20/20a) synthase catalyzes the synthesis of 5,6-dihydro uridine (D) via the reduction of C5,6. It is responsible for half of the wild-cellular tRNA modifications (Bishop et al. 2002 )