Ketosynthase domain probes identify two subclasses of fungal polyketide synthase genes

Analysis of fungal polyketide synthase gene sequences suggested that these might be divided into two subclasses, designated WA-type and MSAS-type, Two pairs of degenerate PCR primers (LC1 and LC2c, LC3 and LC5c) were designed for the amplification of ketosynthase domain fragments from fungal PKS gen es in each of these subclasses. Both primer pairs were shown to amplify one or more PCR products from the genomes of a range of ascomycetous Deuteromy cetes and Southern blot analysis confirmed that the products obtained with each pair of primers emanated from distinct genomic loci. PCR products obta ined from Penicillium patulum and Aspergillus parasiticus with the LC1/2c p rimer pair and from Phoma sp. C2932 with both primer pairs were cloned and sequenced; the deduced protein sequences were highly homologous to the keto synthase domains of other fungal PKS genes. Genes from which LC1/2c fragmen ts were amplified (WA-type) were shown by a phylogenetic analysis to be clo sely related to fungal PKS genes involved in pigment and aflatoxin biosynth etic pathways, whereas the gene from which the LC3/5c fragment was amplifie d (MSAS-type) was shown to be closely related to genes encoding 6-methylsal icylic acid synthase (MSAS), The phylogenetic tree strongly supported the d ivision of fungal PKS genes into two subclasses. The LC-series primers may be useful molecular tools to facilitate the cloning of novel fungal polyket ide synthase genes, (C) 1999 Academic Press.