Involved in the pyrimidine salvage pathway (Probable) (PubMed:21828290, PubMed:31101721, PubMed:31907295). Phosphorylates uridine to uridine monophosphate (UMP) (PubMed:21828290, PubMed:31101721, PubMed:31907295). Phosphorylates cytidine to cytidine monophosphate (CMP) (PubMed:31101721). Does not possess uracil phosphoribosyltransferase (UPRTase) activity that catalyzes the conversion of uracil and 5-phospho-alpha-D-ribose 1-diphosphate (PRPP) to UMP and diphosphate (PubMed:19563437, PubMed:21828290, PubMed:31101721). ATP + cytidine = ADP + CMP + H(+) ATP + uridine = ADP + H(+) + UMP Pyrimidine metabolism; CTP biosynthesis via salvage pathway; CTP from cytidine: step 1/3. Pyrimidine metabolism; UMP biosynthesis via salvage pathway; UMP from uridine: step 1/1. Aggregates in granular precipitates restricted to the cytoplasm, when expressed in transfected cells. Expressed in roots, leaves and stems. No visible phenotype under normal growth conditions (PubMed:17143579, PubMed:19563437). No decrease in uracil phosphoribosyltransferase activity (PubMed:17143579, PubMed:19563437). Loss of sensitivity to 5'-fluorouracil and 5'-fluorouridine (PubMed:17143579, PubMed:21828290). In the N-terminal section; belongs to the uridine kinase family. In the C-terminal section; belongs to the UPRTase family. Was prevsiouly characterized as an enzyme that possesses uracil phosphoribosyltransferase (UPRT) activity (PubMed:17143579). Further publications show a lack of such activity (PubMed:19563437, PubMed:21828290).