Prenyltransferase; part of the gene cluster that mediates the biosynthesis of clavilactone A, a meroterpenoid that features a unique benzo-fused ten-membered carbocyclic ring unit with an alpha,beta-epoxy-gamma-lactone moiety, forming an intriguing 10/5/3 tricyclic nested skeleton. ClaR, ClaS and ClaT are sufficient to produce clavilactone A. Within the pathway, claS acts as an atypical UbiA prenyltransferase that transfers geranyl pyrophosphate (GPP) to hydroquinone (HYQ) instead of p-hydroxybenzoic acid (PHB), producing the first intermediate geranylhydroquinone. The cytochrome P450 monooxygenase claR then catalyzes the diradical coupling reaction between the intramolecular hydroquinone and allyl moieties to form the benzo-fused ten-membered carbocyclic ring unit of wigantol. Finally the cytochrome P450 monooxygenase claT exquisitely and stereoselectively assembles the alpha,beta-epoxy-gamma-lactone moiety, producing clavilactone A via arnebinol A