Our long-term goal is to prevent liver cancer by eliminating dietary aflatoxin and human exposure to this mycotoxin in food. In past research, we made significant progress towards this long-term goal and accomplished two short-term goals. (1) We identified key components in the genetic switch that activate aflatoxin gene expression and developed a comprehensive model that predicts the detailed mechanisms by which the switch regulates the timing and level of aflatoxin synthesis. (2) We identified several fungal and plant metabolites that block aflatoxin accumulation and gene expression. In the next phase of this research, we will analyze two key components of the switch mechanism in sufficient detail to identify specific steps that are susceptible to control. Using this information, we will continue to identify and test promising natural plant and fungal compounds that block aflatoxin synthesis. This research approach will allow us to confirm or modify key steps in the regulatory model and will fill a critical knowledge gap in our understanding of aflatoxin synthesis specifically and in control of complex gene clusters in general. This approach will also assist efforts to formulate and apply effective strategies to block aflatoxin synthesis on susceptible crops. Based on our model of the genetic switch, we present two central hypotheses: 1) active CRE1bp complexes recruit proteins necessary for initiation of aflatoxin gene expression (AflR and HAT); 2) the timing and level of aflatoxin gene activation is in part controlled by the initiation and spread of histone H4 acetylation in the aflatoxin gene cluster. To address these hypotheses, we propose to accomplish two Specific Aims. 1. Analyze the role of CRE1bp in aflatoxin gene activation. 2. Analyze the role of histone H4 acetylation in aflatoxin gene activation. As part of the proposed work for each specific aim, we will identify new inhibitors of aflatoxin synthesis and determine the specific mechanisms by which these and previously identified inhibitors block aflatoxin synthesis. Our work will allow us to effectively control aflatoxin synthesis on food and feed crops - this outcome will have a large positive impact on human health by providing one practical strategy to reduce liver cancer incidence. PUBLIC HEALTH RELEVANCE: As part of the proposed work, we will identify new inhibitors of aflatoxin synthesis and determine the specific mechanisms by which these and previously identified inhibitors block aflatoxin synthesis. Our work will allow us to effectively control aflatoxin synthesis on food and feed crops. This outcome will have a large positive impact on human health by providing one practical strategy to reduce liver cancer incidence.