Geranylgeranyl pyrophosphate (GGPP) mainly participates in post-translational modification for various proteins including Rho/Rac, Rap and Rab families, as well as in regulation for cell apoptosis. Geranylgeranyl pyrophosphate synthase (GGPPS), which catalyzes the condensation reaction between farnesyl diphosphate and isopentenyl diphosphate, is the key enzyme for synthesizing GGPP. We report the isolation of a gene transcript showing high homology withDrosophila GGPPS cDNA. The transcript is 1 466 bp in length and contains an intact open reading frame (ORF) ranging from nt 239 to 1 138. This ORF encodes a deduced protein of 300 residues with calculated molecular weight of 35 ku. The deduced protein shows 57.5% identity and 75% similarity withDrosophila GGPPS, and contains five characteristic domains of prenyltransferases. Northern hybridization revealed that humanGGPPS was expressed highest in heart, and moderately in spleen, testis, brain, placenta, lung, liver, skeletal muscle, kidney and pancreas. No obvious bands were detected in other examined tissues. TheGGPPS gene was located on human chromosome 1q43 by Radiation Hybrid mapping method. It was proved that there was a putative predisposing gene for prostate cancer in this region, and that analogs of GGPP can inhibit the geranylgeranylation of p21rap protein in PC-3 prostate cancer cell lines. These facts suggest thatGGPPS may be one of the candidate genes for prostate cancer.