Phylogenetic analysis of polyketide synthase genes fromAspergillus ochraceus

A number of polyketide synthase gene sequences fromAspergillus ochraceus were isolated by both SSH-PCR and degenerate PCR. The deduced amino acid sequences of the corresponding clonedpks DNA fragments were then aligned with the amino acid sequences of other polyketide synthase enzymes. One of thesepks genes is essential for ochratoxin A biosynthesis (OTA-PKS). The OTA-PKS was most similar to methylsalicylic acid synthase (MSAS) type PKS proteins based on the alignment of the ketosynthase domains while if the acyl transferase domains were aligned it appeared to be more similar to PKS enzymes fromCochliobolus heterostrophus. The three PKS proteins identified by degenerate PCR were all from different PKS types, one was a MSAS type enzyme, the second was similar to the PKS proteins involved in lovastatin biosynthesis while the third was not similar to any of the other phylogenetic groupings. Data is presented which suggests that the use of phylogenetic analysis to predict the function of PKS proteins/genes is likely to be significantly enhanced by analyzing more than one domain of the protein.