STRUCTURE AND FUNCTION OF FAS-1A, A GENE ENCODING A PUTATIVE FATTY-ACID SYNTHETASE DIRECTLY INVOLVED IN AFLATOXIN BIOSYNTHESIS IN ASPERGILLUS-PARASITICUS

A novel gene, fas-1A, directly involved in aflatoxin B1 (AFB1) biosynt hesis, was cloned by genetic complementation of an Aspergillus parasit icus mutant strain, UVM8, blocked at two unique sites in the AFB1 bios ynthetic pathway, Metabolite conversion studies localized the two gene tic blocks to early steps in the AFB1 pathway (nor-1 and fas-1A) and c onfirmed that fas-1A is blocked prior to nor-1, Transformation of UVM8 with cosmids NorA and NorB restored function in nor-1 and fas-1A, res ulting in synthesis of AFB1. An 8-kb SacI subclone of cosmid NorA comp lemented fas-1A only, resulting in accumulation of norsolorinic acid, Gene disruption of the fas-1A locus blocked norsolorinic acid accumula tion in A, parasiticus B62 (nor-1), which normally accumulates this in termediate, These data confirmed that fas-1A is directly involved in A FB1 synthesis. The predicted amino acid sequence of fas-1A showed a hi gh level of identity with extensive regions in the enoyl reductase and malonyl/palmityl transferase functional domains in the beta subunit o f yeast fatty acid synthetase. Together, these data suggest that fas-1 A encodes a novel fatty acid synthetase which synthesizes part of the polyketide backbone of AFB1, Additional data support an interaction be tween AFB1 synthesis and sclerotium development.