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Comment

(from Uniprot) Non-reducing polyketide synthase\; part of the gene cluster A that mediates the biosynthesis of austinol and dehydroaustinol, two fungal meroterpenoids. The first step of the pathway is the synthesis of 3,5-dimethylorsellinic acid by the polyketide synthase ausA. 3,5-dimethylorsellinic acid is then prenylated by the polyprenyl transferase ausN. Further epoxidation by the FAD-dependent monooxygenase ausM and cyclization by the probable terpene cyclase ausL lead to the formation of protoaustinoid A. Protoaustinoid A is then oxidized to spiro-lactone preaustinoid A3 by the combined action of the FAD-binding monooxygenases ausB and ausC, and the dioxygenase ausE. Acid-catalyzed keto-rearrangement and ring contraction of the tetraketide portion of preaustinoid A3 by ausJ lead to the formation of preaustinoid A4. The aldo-keto reductase ausK, with the help of ausH, is involved in the next step by transforming preaustinoid A4 into isoaustinone which is in turn hydroxylated by the P450 monooxygenase ausI to form austinolide. Finally, the cytochrome P450 monooxygenase ausG modifies austinolide to austinol. Austinol can be further modified to dehydroaustinol which forms a diffusible complex with diorcinol that initiates conidiation. Due to genetic rearrangements of the clusters and the subsequent loss of some enzymes, the end products of the Emericella nidulans austinoid biosynthesis clusters are austinol and dehydroaustinol, even if additional enzymes, such as the O-acetyltransferase ausQ and the cytochrome P450 monooxygenase ausR are still functional. Other strains: Emericella nidulans (strain FGSC A4 \/ ATCC 38163 \/ CBS 112.46 \/ NRRL 194 \/ M139) (Aspergillus nidulans) || Only 2404-2445\/ 2476 residu a\/b hydrolase