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.Indeed, Dihydrouridine (D) appears as important in the maintenance of tRNA stability
(Alexandrov et al. 2006 ). It appears acting as a quality control marker, with its absence provoking rapid tRNA decays. D is generated post-transcriptionally by Dus enzymes and it is found in different positions of tRNAs. Dus3 modifies U47 in different tRNA substrates.
Dus3 catalyzes the D formation of tRNA through reduction of uracil base with flavin mononucleotide (FMN) as a cofactor. Not essential enzyme. Dus3 modifies all tRNAs with U at position 47, with the exception of tRNAPhe1, Phe2, and Lys1.