Involved in the pyrimidine salvage pathway (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. No visible phenotype (PubMed:19563437). No decrease in uracil phosphoribosyltransferase activity (PubMed:19563437). Loss of sensitivity to 5'-fluorouracil and 5'-fluorouridine (PubMed:21828290). In the N-terminal section; belongs to the uridine kinase family. In the C-terminal section; belongs to the UPRTase family.