Catalyzes the synthesis of dihydrouridine, a modified base found in the D-loop of most tRNAs (PubMed:34798057). Also able to mediate dihydrouridylation of some mRNAs, thereby affecting their translation (PubMed:34798057). 5,6-dihydrouridine(16) in tRNA + NADP(+) = H(+) + NADPH + uridine(16) in tRNA 5,6-dihydrouridine(16) in tRNA + NAD(+) = H(+) + NADH + uridine(16) in tRNA 5,6-dihydrouridine(17) in tRNA + NAD(+) = H(+) + NADH + uridine(17) in tRNA 5,6-dihydrouridine(17) in tRNA + NADP(+) = H(+) + NADPH + uridine(17) in tRNA a 5,6-dihydrouridine in mRNA + NAD(+) = a uridine in mRNA + H(+) + NADH a 5,6-dihydrouridine in mRNA + NADP(+) = a uridine in mRNA + H(+) + NADPH Belongs to the Dus family. Dus1 subfamily.