Dihydrouridine

Dihydrouridine is a pyrimidine which is the result of adding two hydrogen atoms to a uridine, making it a fully saturated pyrimidine ring with no remaining double bonds. Dihydrouridine is found in tRNA and rRNA molecules.

Because it is non-planar, D disturbs the stacking interactions in helices and destabilizes the RNA structure. Furthermore, Dalluge et al. also showed that replacement of a uridine by a 5,6-dihydrouridine stabilizes the C2’-endo sugar conformation, which is more flexible then the C3’-endo conformation, and this effect is propagated to the 5’-neighboring residue. Thus, while pseudouridine and 2’-O-methylations stabilize the local RNA structure, D appears to do the opposite. This proposal is supported by the observation of high 5,6-dihydrouridine levels in the tRNA of organisms that grow at low temperatures (psychrophiles). A higher percentage of D in these organisms would provide the necessary, local, flexibility of the tRNA at or below the freezing point.