(Microbial infection) Required for optimal replication of E.chaffeensis in the immune tissues, hemocytes, and fat body. ATP + uridine = ADP + H(+) + UMP ATP + cytidine = ADP + CMP + H(+) 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. (Microbial infection) After infection with E.chaffeensis, results in reduced bacterial replication rate and increased survival (PubMed:22851751). RNAi-mediated knockdown in the whole organism, in the fat body or hemocytes results in a similar phenotype to the genetic knockout (PubMed:23306065). However, knockdown in the eye, salivary gland or wing has no effect (PubMed:23306065). Belongs to the uridine kinase family.