Mevalonate kinase [ATP:(R)-mevalonate 5-phosphotransferase, EC 2.7.1.36] may be a regulatory site in the cholesterol biosynthetic pathway, and a mutation in the gene coding for this enzyme is thought to cause the genetic disease mevalonic aciduria. To characterize this enzyme, a rat liver cDNA library was screened with a monospecific antibody, and a 1.7-kilobase cDNA clone coding for mevalonate kinase was isolated. A mutation in the gene coding for mevalonate kinase is presumed to be the cause of the recently discovered genetic disease mevalonic aciduria (4, 5). The genetic disease is transmitted as an autosomal recessive trait, and there are six reported cases (6). Subjects with mevalonic aciduria have extremely high levels of mevalonate in their plasma and urine, and cells from these subjects have <10% of the normal levels of mevalonate kinase activity (4-6). As a first step in identifying the molecular defect causing mevalonic aciduria and to study the regulation of mevalonate kinase activity, we have isolated and characterized a cDNA clone coding for rat mevalonate kinase.* Data are also presented to show that long-term regulation of enzyme activity in rat liver is controlled by changes in the levels of mevalonate kinase mRNA. MATERIALS AND METHODSPreparation of the Antiserum. Monospecific antisera to rat mevalonate kinase was prepared in rabbits by using the purified enzyme (3), and the IgG fraction was collected by affinity chromatography (7).Isolation of a cDNA Clone Coding for Mevalonate Kinase. A Agtll cDNA library (8) derived from mRNA purified from the livers of rats treated with diets containing 5% cholestyramine and 0.1% lovastatin was kindly provided by Peter Edwards (UCLA). Positive clones were identified by immunoscreening (9). To obtain a full-length cDNA clone, the cDNA insert from one of the clones was isolated and radiolabeled by random priming (10) to a specific activity of 109 cpm per Ag ofDNA. The radiolabeled probe was used to screen -2 x 105 recombinants. Plaque hybridization was performed as described (8), after which the filters were washed at 680C with 2 x SSC (1x SSC = 0.15 M NaCI/0.015 M sodium citrate, pH 7) containing 0.1% SDS, followed by washes with 0.lx SSC containing 0.1% SDS. Fifteen cDNA clones were isolated. The cDNA inserts were subcloned into the pGEM-3Z vector (Promega) for restriction enzyme mapping or into M13 vectors for DNA sequencing.DNA Sequencing. The DNA sequence of the cDNA was determined by the dideoxynucleotide chain-termination method (11). Sequencing reactions using the Klenow fragment of DNA polymerase I (New England Biolabs) or the modified T7 DNA polymerase (Sequenase, United States Biochemicals) were performed following the manufacturer's protocol. The DNA and protein sequences were aligned using the Intelligenetics computer program, and the EMBL/ GenBank and PIR data bases were searched for homologies to the DNA sequence and protein sequence of mevalonate kinase.Expression of the Mevalonate Kinase cDNA in Saccharomyces cerevisiae. A 1.3-kilobase...

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