Catalyzes a late step in pyrimidine degradation. Converts N-carbamoyl-beta-aminoisobutyrate and N-carbamoyl-beta-alanine (3-ureidopropanoate) to, respectively, beta-aminoisobutyrate and beta-alanine, ammonia and carbon dioxide. Involved in the recycling of nitrogen from nucleobases to general nitrogen metabolism. 3-(carbamoylamino)propanoate + 2 H(+) + H2O = beta-alanine + CO2 + NH4(+) 3-(carbamoylamino)-2-methylpropanoate + 2 H(+) + H2O = (R)-3-amino-2-methylpropanoate + CO2 + NH4(+) Amino-acid biosynthesis; beta-alanine biosynthesis. Homodimer, homotetramer, homooctamer; can also form higher homooligomers. Up-regulated between days 3 and 5 after germination and during senescence. Up-regulated by nitrogen limitation. No visible phenotype, but unable to grow on uracil as sole nitrogen source. Belongs to the carbon-nitrogen hydrolase superfamily. BUP family. Truncated N-terminus.