The objective of these studies will be to determine how the levels of aminoacyl-tRNA synthetases are regulated in a higher eukaryote, Bombyx mori. This organism will be employed because its silkgland specializes its protein synthetic apparatus for the synthesis of two unusual protein (fibroin and sericin). The goal of the project will be accomplished by purifying three aminoacyl-tRNA synthetases (for glycine, alanine, and serine) and using the purified proteins to develop quantitative immunological assays for the enzyme protein. The levels of these enzymes, will be determined in the silkgland and other organs to determine if the observed specialization of tRNAs for fibroin and sericin production is reflected in the levels of the cognate aminoacyl-tRNA synthetases. This approach will make it possible to determine if the observed changes in enzyme activity during silkgland development result from changes in enzyme specific activity or from increased levels of enzyme protein. The long term goal of these studies will be the elucidation of basic cellular processes that control the levels of these enzymes. An additional objective will be the cloning of aminoacyl-tRNA synthetase genes.