This proposal describes biochemical experiments to test Strehler's codon restriction hypothesis of development and aging in Drosophila. I propose to determine: (1) whether certain tRNA genes are deleted or rearranged in the DNA of old Drosophila flies, in minute mutants and life-span mutants; (2) the state of nucleotide modification or of the 3'-terminal C-C-A sequence in tRNA from old flies; and (3) the ability of Drosophila aminoacyl-tRNA synthetases (from young and old flies) to aminoacylate all Drosophila tRNAs. All these factors determine the availability of aminoacyl-tRNA for translation, a crucial process for the codon restriction theory.