title: Aflatoxin biosynthesis cluster gene cypA is required for G aflatoxin formation.
abstract: Aspergillus flavus isolates produce only aflatoxins B1 and B2, while Aspergillus parasiticus and Aspergillus nomius produce aflatoxins B1, B2, G1, and G2. Sequence comparison of the aflatoxin biosynthesis pathway gene cluster upstream from the polyketide synthase gene, pksA, revealed that A. flavus isolates are missing portions of genes (cypA and norB) predicted to encode, respectively, a cytochrome P450 monooxygenase and an aryl alcohol dehydrogenase. Insertional disruption of cypA in A. parasiticus yielded transformants that lack the ability to produce G aflatoxins but not B aflatoxins. The enzyme encoded by cypA has highest amino acid identity to Gibberella zeae Tri4 (38%), a P450 monooxygenase previously shown to be involved in trichodiene epoxidation. The substrate for CypA may be an intermediate formed by oxidative cleavage of the A ring of O-methylsterigmatocystin by OrdA, the P450 monooxygenase required for formation of aflatoxins B1 and B2.
authors.affiliation: Southern Research Center, Agricultural Regional Research Service, U.S. Department of Agriculture, New Orleans, Louisiana 70179, USA. ehrlich@srrc.ars.usda.gov
authors.forename: Kenneth C
authors.initials: KC
authors.lastname: Ehrlich
authors.forename: Perng-Kuang
authors.initials: PK
authors.lastname: Chang
authors.forename: Jiujiang
authors.initials: J
authors.lastname: Yu
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Cotty
mesh_terms: D000348:Aflatoxins / Q000096:biosynthesis* / Q000737:chemistry; D000595:Amino Acid Sequence; D001230:Aspergillus / Q000201:enzymology* / Q000235:genetics; D001231:Aspergillus flavus / Q000201:enzymology / Q000235:genetics; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D008969:Molecular Sequence Data; D005810:Multigene Family; D017422:Sequence Analysis, DNA
chemical_list: D000348:Aflatoxins; D005656:Fungal Proteins; C027955:aflatoxin G1; C029754:aflatoxin G2; D003577:Cytochrome P-450 Enzyme System