The specific aims of this proposal are directed toward a molecular characterization of the stunted (stuA) gene, a modifier of conidiophore development in Aspergillus nidulans. The stunted gene is a member of a group of potential regulatory genes that are arranged in a hierarchical order and that control normal development during conidiation. Mutations in this gene have a profound affect upon conidiophore structure, a result of aberrant progression though the normal developmental program. Molecular genetic techniques will be used to clone and physically characterize the stunted gene in order to begin an investigation of the gene product's biochemical function; to elucidate the temporal expression of this gene during development in the wild type strain and in other developmental mutants; to investigate the affects of experimentally altered stunted gene expression upon conidiophore development and to isolate novel stuA alleles. Double mutants will be generated for the purpose of investigating potential interactions, at the molecular level, of genes responsible for normal asexual reproduction and to relate these interactions to structure formation. %%% A fundamental problem in biology is the elucidation of molecular mechanisms that mediate cell differentiation and the organization of cell types during morphogenesis. The filamentous fungi are an important group of organisms that have been extremely useful for studies that address development in eucaryotes. Although many of these fungi are propagated by asexually produced and aerially dispersed conidia (spores), very little is known about the biochemical and genetic mechanisms that mediate coordinately regulated gene expression and cellular differentiation during asexual reproduction.