Aflatoxins comprise a group of polyketide-derived carcinogenic mycotoxins produced by
Aspergillus parasiticus and
Aspergillus flavus. By transformation with a disruption construct, pXX, we disrupted the aflatoxin pathway in
A. parasiticus SRRC 2043, resulting in the inability of this strain to produce aflatoxin intermediates as well as a major yellow pigment in the transformants. The disruption was attributed to a single-crossover, homologous integration event between pXX and the recipient
A. parasiticus genome at a specific locus, designated
pksA. Sequence analysis suggest that
pksA is a homolog of the
Aspergillus nidulans wA gene, a polyketide synthase gene involved in conidial wall pigment biosynthesis. The conserved
β-ketoacyl synthase, acyltransferase and acyl carrier-protein domains were present in the deduced amino acid sequence of the
pksA product. No
β-ketoacyl reductase and enoyl reductase domains were found, suggesting that
pksA does not encode catalytic activities for processing
β-carbon similar to those required for long chain fatty acid synthesis. The
pksA gene is located in the aflatoxin pathway gene cluster and is linked to the
nor-1 gene, an aflatoxin pathway gene required for converting norsolorinic acid to averantin. These two genes are divergently transcribed from a 1.5 kb intergenic region. We propose that
pksA is a polyketide synthase gene required for the early steps of aflatoxin biosynthesis.
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