Proton-coupled transporter that transports a wide spectrum of oxo derivatives of heterocyclic nitrogen compounds, including allantoin, uric acid and xanthine, but not adenine. Mediates transport of uracil and 5-fluorouracil (a toxic uracil analog). Proton-coupled transporter that transports a wide spectrum of oxo derivatives of heterocyclic nitrogen compounds, including allantoin, xanthine and uracil. Optimum pH is 4.7. Expressed in lateral roots, rosette leaves, stems, stipules, flower stigma, pedicels and the connective tissue between pollen sacks. Belongs to the plant ureide permease (TC 2.A.7.19) family. Truncated N-terminus.