MOLECULAR-CLONING OF HUMAN PHOSPHOMEVALONATE KINASE AND IDENTIFICATION OF A CONSENSUS PEROXISOMAL TARGETING SEQUENCE

Two overlapping cDNAs which encode human liver phosphomevalonate kinas e (PMKase) were isolated. The human PMKase cDNAs predict a 191-amino a cid protein with a molecular weight of 21,862, consistent with previou s reports for mammalian PMKase (M(r) = 21,000 - 22,500), Further verif ication of the clones was obtained by expression of PMKase activity in bacteria using a composite 1024-base pair cDNA clone. Northern blot a nalysis of several human tissues revealed a doublet of transcripts at approximately 1 kilobase (kb) in heart, liver, skeletal muscle, kidney , and pancreas and lower but detectable transcript levels in brain, pl acenta, and lung. Analysis of transcripts from human lymphoblasts subc ultured in lipid-depleted sera (LDS) and LDS supplemented with lovasta tin indicated that PMKase gene expression is subject to regulation by sterol at the level of transcription. Southern blotting indicated that PMKase is a single copy gene covering less than 15 kb in the human ge nome. The human PMKase amino acid sequence contains a consensus peroxi somal targeting sequence (PTS-1), Ser-Arg-Leu, at the C terminus of th e protein. This is the first report of a cholesterol biosynthetic prot ein which contains a consensus PTS-1, providing further evidence for t he concept that early cholesterol and nonsterol isoprenoid biosynthesi s may occur in the peroxisome.