DESCRIPTION: The long-term goal of the proposed research is to understand how the sterigmatocystin(ST) and aflatoxin (AF) biosynthetic pathways are genetically regulated. These highly toxic and carcinogenic mycotoxins are produced as a result of secondary metabolism by filamentous fungi belonging to the genus Aspergillus. Since among the mycotoxin producing fungi A. nidulans is the most highly developed for genetic analysis and for use of recombinant DNA techniques, we propose to use this organism as a model system to study the ST/AF metabolic pathways. We have discovered a cluster of 25 genes, which are coordinately regulated and developmentally associated with ST biosynthesis, and it contains most, if not all the genes needed for ST biosynthesis. Our goal is to study genetic regulation of the ST pathway. Our aims are: (1) to determine whether a presumptive regulatory gene stcD in the ST gene cluster is involved in the genetic regulation of ST biosynthesis. This gene exhibits a unique expression pattern among the ST cluster genes and its sequence predicts a polypeptide similar to known transcription factors. Experiments are designed to test the hypothesis that stcD may be involved in the regulation of the ST pathway. (2) To examine the hypothesis that the species specific genetic regulator of the AF/ST pathways, aflR, determines the ST biosynthetic response to different cultural conditions. (3) To discover, isolate and characterize other, unknown genes associated with genetic regulation of aflR, the activator gene for ST biosynthesis, which are located outside the ST gene cluster, using a specially developed mutant selection strain. While secondary metabolism is known to be involved in so called luxury functions associated with cell differentiation in animals, and in the production of antibiotics and toxins in actinomycetes, bacteria and fungi, little is known about how secondary metabolism is genetically regulated. Understanding the mechanisms through which various environmental and physiological factors influence the transription activation of the ST pathway regulator gene, aflR, is significant and an essential step in designing rational approaches to blocking undesirable ST and AF production.