O-acetyltransferase; part of the gene cluster that mediates the biosynthesis of the prenylated pyrroloindoline diketopiperazine acetylaszonalenin (PubMed:19001367). The first step in the pathway is the formation of (R)-benzodiazepinedione by condensation of tryptophan and anthranilic acid catalyzed by the non-ribosomal peptide synthetase anaPS (PubMed:19001367). The prenyltransferase anaPT then converts (R)-benzodiazepinedione to aszonalenin in the presence of dimethylallyl diphosphate (DMAPP) via C3-prenylation (PubMed:19001367, PubMed:20165805). The last step in the biosynthesis of acetylaszonalenin via acetylation of aszonalenin at position N1 catalyzed by anaAT (PubMed:19001367, PubMed:20165805). Alkaloid biosynthesis. Monomer. Belongs to the fumigaclavine B O-acetyltransferase family.