Uracil–DNA Glycosylase from Beta vulgaris: Properties and Response to Abiotic Stress

Uracil−DNA glycosylases (UNGs) are DNA repair enzymes responsible for the removal of uracil, a canonical RNA nucleobase, from DNA, where it appears through cytosine deamination or incorporation from the cellular dUTP pool. While human and Escherichia coli UNGs have been extensively investigated, much less is known about their plant counterparts, of which UNGs from Arabidopsis thaliana are the only studied examples. Here, we show that in sugar beet (Beta vulgaris L.), an important crop species, cold and salt stress induce the expression of the UNG gene (BvUNG) and modulate the level of the uracil-excising activity in the roots. Purified recombinant BvUNG efficiently removes uracil from DNA both in vitro and in an E. coli reporter strain but does not excise 5-hydroxyuracil, 5,6-dihydrouracil, or 5-hydroxymethyluracil. The activity is abolished by Ugi, a protein UNG inhibitor from PBS1 bacteriophage, and by a mutation of a conserved active site His residue. Structural modeling shows the presence of a disordered N-tail prone to undergo phase separation, followed by a long α helix oriented differently from its counterpart in human UNG. Overall, BvUNG is a functional uracil–DNA glycosylase that might participate in the response to abiotic stress.