The objective of the proposed research is to study several aspects of the regulation of gene expression in a higher eukaryotic form. The maroon-like mutants in Drosophila in conunction with mutations of several other separable loci provide an excellent system for such an investigation because they include structural genes, a cofactor- producing gene and other genes whose true function is yet unknown. The maroon-like mutations affect the activities of three disparate enzymes, while the other loci affect the expression of one or more of the three enzymes. A unique nutritional selective system has been used for high resolution fine structural analysis of two of the loci and will be useful for similar studies of another one of the loci as well as for the selection of an array of mutations at three of the loci. The product of the maroon-like locus as well as those of the other loci will be isolated and characterized, so that the molecular basis of the interactions of these gene products may be understood.