Catalyzes the phosphorylation of pyrimidine nucleoside monophosphates at the expense of ATP. Plays an important role in de novo pyrimidine nucleotide biosynthesis. Has preference for UMP and dUMP as phosphate acceptors, but can also use CMP, dCMP, AMP, GMP, dGMP and dTMP. ATP and dATP are the best phosphate donors, but can also use GTP, dGTP, dCTP, and dTTP to some degree. ATP + UMP = ADP + UDP Binds 1 Mg(2+) ion per monomer. Optimum pH is 6-9.5. Monomer. Predominantly cytoplasmic. Consists of three domains, a large central CORE domain and two small peripheral domains, NMPbind and LID, which undergo movements during catalysis. The LID domain closes over the site of phosphoryl transfer upon ATP binding. Assembling and dissambling the active center during each catalytic cycle provides an effective means to prevent ATP hydrolysis. Present with 1500 molecules/cell in log phase SD medium. Belongs to the adenylate kinase family. UMP-CMP kinase subfamily. There is controversy about the substrate specificity of the enzyme. Next to the primary substrate UMP, PubMed:1333436 and Ref.8 report that the enzyme accepts also CMP and AMP as nucleoside monophosphates, but not GMP, whereas PubMed:2172245 and PubMed:8391780 report activity with GMP and dTMP, but not AMP or CMP.