Conidiation of the filamentous fungus Aspergillus nidulans is a developmental program of cell differentiation which culminates in the production of spore-bearing structures called conidiophores. The initiation of this program od development serves as a model system for the study of the inhibition of proliferative growth and the onset of cellular differentiation both of which are relevant to cancer studies. Many closely related species of Aspergillus function as human pathogens or dangerous contaminants of food crops. Understanding the regulation of growth and development in A. nidulans may aid in the development of drugs or control programs in the pathogenic species of Aspergillus. The flbD gene has been shown to be important for the normal function of an initiation pathway that leads to development. It is probable that FlbD functions as a transcription factor during developmental initiation because the N- terminal region of FlbD is very similar to the DNA binding regions of the Myb family of transcription factors, including the protooncogene c-myb. It is proposed that to investigate the pathways leading to development and to further define the role of FlbD, target sites in DNA, to which FlbD binds specifically, will be identified. This will facilitate the identification of genes whose expression is regulated by FlbD during development. Second, in order to further define the pathways which signal development, suppressor mutants will be isolated which can bypass the requirement for FlbD for normal conidiation. Lastly, dominant mutations in FlbD will be generated which may identify regions which are important for its regulation or activity.