This invention provides: (A) a protein the sequence of which is in FIG. 8 (SEQ. ID n.degree. 14), or a fragment thereof having at least 15 amino acids, or a variant thereof, having at least 70% identity with FIG. 8 (SEQ. ID n.degree. 14) over a length of at least 400 amino acids; (B) a peptide comprising a fragment of salutaridinol 7-O-acetyltransferase of at least 6 consecutive amino acids not present in other plant acetyltransferases as in FIG. 2 (SEQ. IDs n.degree. 8 to 12); (C) a nucleic acid (i) the sequence of which is in FIG. 9 (SEQ. ID n.degree. 13) or FIG. 10 (SEQ. ID n.degree. 15), or (ii) a fragment thereof of at least 45 nucleotides, or (iii) a variant thereof, having at least 70% identity with FIG. 9 (SEQ. ID n.degree. 13) or FIG. 10 (SEQ. ID n.degree. 15) over a length of at least 1200 bases, or (iv) a sequence complementary to (i), (ii) or (iii); or (v) the RNA equivalent of any of (i), (ii), or (iii); (D) a nucleic acid comprising a fragment of a salutaridinol 7-O-acetyltransferase gene of at least 18 consecutive nucleotides unique to the salutaridinol 7-O-acetyltransferase gene from the 5' or 3' untranslated regions in FIG. 9 (SEQ. ID n.degree. 13), or a sequence complementary thereto. This invention also provides methods for producing pentacyclic morphinan alkaloids and thebaine.