uracil 5-bromouracil 5-bromopyrimidine-2,4(1H,3H)-dione 5-bromo-2,4(1H,3H)-pyrimidinedione A pyrimidine having keto groups at the 2- and 4-positions and a bromo group at the 5-position. Used mainly as an experimental mutagen. 5-bromopyrimidine-2,4(1H,3H)-dione 5-BU bromouracil 1,2,3,4-tetrahydro-5-bromo-2,4-pyrimidinedione 5-BrU mutagen pyrimidines nucleobase analogue