Catalyzes the conversion of ent-copalyl diphosphate to the gibberellin precursor ent-kaur-16-ene. ent-copalyl diphosphate = diphosphate + ent-kaur-16-ene Binds 3 Mg(2+) ions per subunit. Optimum pH is 6.8-7.5. Plant hormone biosynthesis; gibberellin biosynthesis. Abundant in most tissues. Present in low amounts in mature cotyledons. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). The N-terminus is blocked. Belongs to the terpene synthase family.