Catalyzes the second step of the reductive pyrimidine degradation, the reversible hydrolytic ring opening of dihydropyrimidines. Can catalyze the ring opening of 5,6-dihydrouracil to N-carbamoyl-alanine and of 5,6-dihydrothymine to N-carbamoyl-amino isobutyrate. Involved in the recycling of nitrogen from nucleobases to general nitrogen metabolism. 5,6-dihydrouracil + H2O = 3-(carbamoylamino)propanoate + H(+) Binds 2 Zn(2+) ions per subunit. Amino-acid biosynthesis; beta-alanine biosynthesis. Homotetramer. Up-regulated between days 3 and 12 after germination and during senescence. Up-regulated by nitrogen limitation. Carboxylation allows a single lysine to coordinate two zinc ions. No visible phenotype, but unable to grow on uracil as sole nitrogen source. Belongs to the metallo-dependent hydrolases superfamily. Hydantoinase/dihydropyrimidinase family.