Geranylgeranyl pyrophosphate synthase (GGPS1) is a member of the FPP/GGPP synthase family. GGPS1 is highly expressed in testis, heart and skeletal muscle. GGPS1 is localized in the cytoplasm and has geranylgeranyl diphosphate (GGPP) synthase activity. It catalyzes the trans-addition of the three molecules of IPP onto DMAPP to form geranylgeranyl pyrophosphate, an important precursor of carotenoids and geranylated proteins. Other transcriptional splice variants have been found.