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-carbamyl-alanine and of 5,6-dihydrothymine to N-carbamyl-amino isobutyrate. 5,6-dihydrouracil + H2O = 3-(carbamoylamino)propanoate + H(+) Binds 2 Zn(2+) ions per subunit. Homotetramer. Up-regulated by dihydrouracil and N-carbamyl-beta-alanine. Detectable only in cells grown on dihydrouracil and N-carbamyl-beta-alanine as sole nitrogen source. Carboxylation allows a single lysine to coordinate two zinc ions. Belongs to the metallo-dependent hydrolases superfamily. Hydantoinase/dihydropyrimidinase family.