Bifunctional terpene synthase converts DMAPP and IPP, and also GGPP, into variediene as a single product (PubMed:26546087). The C-terminal prenyltransferase (PT) domain of EvVS catalyzes formation of GGPP, whereas the N-terminal terpene cyclase (TC) domain catalyzes the cyclization of GGPP to variediene (PubMed:26546087). The PT domain can also synthesize GFPP from the C5 isoprene units in vitro, while the TC domain is able to cyclize GFPP to the sesterterpene (2E)-alpha-cericerene (PubMed:26546087). (2E,6E)-farnesyl diphosphate + isopentenyl diphosphate = (2E,6E,10E)-geranylgeranyl diphosphate + diphosphate Secondary metabolite biosynthesis; terpenoid biosynthesis. Hexamer. The conserved DDXXD motifs as well as the NSE/DTE motif are important for the catalytic activity, presumably through binding to Mg(2+). In the N-terminal section; belongs to the terpene synthase family. In the C-terminal section; belongs to the FPP/GGPP synthase family.