Department of Biochemistry & Biophysics, University of North Carolina School of Medicine, Chapel Hill 27599-7260, USA.
Uridine kinase is the rate-limiting enzyme in the pyrimidine salvage pathway of all mammalian cells. A cDNA for uridine kinase from mouse brain has been isolated, sequenced, and characterized. This is the first report of a complete nucleotide sequence for mammalian uridine kinase. The isolated cDNA is only 95% complete, missing the first 17 codons. The correct 5'-terminus sequence was obtained from high-stringency screening of a mouse liver genomic DNA library. The translated cDNA sequence encodes a protein of 277 amino acids (Mr 31,068). A truncated form of the cDNA was expressed in Escherichia coli. The expressed protein displayed uridine kinase activity and readily formed a tetramer, the most active form of the wild-type enzyme. Analysis of the amino acid sequence identified the three ATP-binding site consensus motifs. The predicted secondary structure for uridine kinase and the sequence comparison with three kinases having known crystal structures are consistent with uridine kinase having an alpha/beta core structure of the nucleotide-binding fold found in many kinases. We have also isolated and cloned a nonfunctional, processed pseudogene from mouse genomic DNA. This pseudogene sequence is 94% identical with the coding DNA.