Catalyzes the trans-addition of the 3 molecules of isopentenyl diphosphate (IPP) onto dimethylallyl diphosphate (DMAPP) to form geranylgeranyl pyrophosphate (GGPP). GGPP is a precursor for the biosynthesis of many secondary metabolites, including the indole diterpenes nodulisporic acids (NA). dimethylallyl diphosphate + isopentenyl diphosphate = (2E)-geranyl diphosphate + diphosphate (2E)-geranyl diphosphate + isopentenyl diphosphate = (2E,6E)-farnesyl diphosphate + diphosphate (2E,6E)-farnesyl diphosphate + isopentenyl diphosphate = (2E,6E,10E)-geranylgeranyl diphosphate + diphosphate Binds 3 Mg(2+) ions per subunit. Secondary metabolite biosynthesis. Belongs to the FPP/GGPP synthase family.