Uracil phosphoribosyltransferase (UPRT) that catalyzes the conversion of uracil and 5-phospho-alpha-D-ribose 1-diphosphate (PRPP) to UMP and diphosphate. Is probably the only functional UPRT, since the dual-domain proteins of the UKL family seem to lack this activity. diphosphate + UMP = 5-phospho-alpha-D-ribose 1-diphosphate + uracil Binds 1 Mg(2+) ion per subunit. The magnesium is bound as Mg-PRPP. Allosterically activated by GTP. Pyrimidine metabolism; UMP biosynthesis via salvage pathway; UMP from uracil: step 1/1. Slightly induced 12 days after germination. Up-regulated when pyrimidine catabolism is impaired. The N-terminal sequence (1-125) is sufficient to address heterologous proteins to chloroplasts. Growth retardation, pale-green to albino phenotype and flimsy roots with less branching. Loss of uracil phosphoribosyltransferase activity. Belongs to the UPRTase family.