The long-range goal of this research is to elucidate the mechanism of regulation of the Bombyx mori chorion gene family. This is a set of related genes that are under tight temporal control, and produce well-defined, biologically important differentiated products, the structural proteins of the silkmoth eggshell. The particular power of this model system lies in our ability to combine classic genetic analysis with modern molecular techniques. We are seeking to gain a comprehensive picture of the chromosomal organization of the entire chorion family, and to examine the detailed fine structure and developmental expression of selected chorion genes. The specific aims of this proposal are: 1) To extend our chromosomal map of chorion gene clusters, using electrophoretic variants of chorion proteins as genetic markers, to include all possible structural genes in a standard reference strain; 2) To investigate the chromosomal relationship between the chorion structural genes and a closely liked locus, Gr, whose pleiotropic effects on chorion ultrastructure and protein composition suggest that it may be involved in their regulation; 3) To obtain DNA fragments containing chorion genes by application of molecular cloning techniques, in order to examine the arrangement and structure of chorion genes and their flanking sequences; and 4) To use selected chorion gene-containing DNA fragments as hybridization probes to monitor the accumulation and synthesis of specific chorion mRNAs in relation to their translation. This information will be used to determine whether the chorion family is primarily regulated on the transcriptional, posttranscriptional, or translational level.