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Applied and Environmental Microbiology, November 2000, p. 4715-4719, Vol. 66, No. 11
Southern Regional Research Center,
Agricultural Research Service, U.S. Department of Agriculture, New
Orleans, Louisiana 70124
Received 15 March 2000/Accepted 12 August 2000
Two routes for the conversion of 5'-hydroxyaverantin (HAVN) to
averufin (AVF) in the synthesis of aflatoxin have been proposed. One
involves the dehydration of HAVN to the lactone averufanin (AVNN),
which is then oxidized to AVF. Another requires dehydrogenation of HAVN
to 5'-ketoaverantin, the open-chain form of AVF, which then cyclizes
spontaneously to AVF. We isolated a gene, adhA, from the
aflatoxin gene cluster of Aspergillus parasiticus SU-1. The
deduced ADHA amino acid sequence contained two conserved motifs found
in short-chain alcohol dehydrogenases
0099-2240/00/$04.00+0
adhA in Aspergillus
parasiticus Is Involved in Conversion of 5'-Hydroxyaverantin
to Averufin
a glycine-rich loop (GXXXGXG)
that is necessary for interaction with
NAD+-NADP+, and the motif YXXXK, which is found
at the active site. A. parasiticus SU-1, which produces
aflatoxins, has two copies of adhA (adhA1), whereas A. parasiticus SRRC 2043, a strain that accumulates
O-methylsterigmatocystin (OMST), has only one copy.
Disruption of adhA in SRRC 2043 resulted in a strain that
accumulates predominantly HAVN. This result suggests that ADHA is
involved in the dehydrogenation of HAVN to AVF. Those adhA
disruptants that still made small amounts of OMST also accumulated other metabolites, including AVNN, after prolonged culture.
*
Corresponding author. Mailing address: Southern
Regional Research Center, Agricultural Research Service, U.S.
Department of Agriculture, 1100 Robert E. Lee Blvd., New Orleans, LA
70124. Phone: (504) 286-4208. Fax: (504) 286-4419. E-mail:
pkchang{at}nola.srrc.usda.gov.
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