In S. typhimurium the sites of mutations causing feedback resistance of anthranilate synthetase and phosphoribosyl transferase will be mapped in the first and second genes of the tryptophan operon. The mutations will be related to the structural alterations in the enzymes by "fingerprinting" peptide fragments. The basis for suppression of promoter mutations and stimulation of nonmutant operons by supX-mutations will be studied by in vitro protein and mRNA synthesizing systems, by study of the structures of the mutant promoters, by the interactions with regulatory mutations, and by examination of the subunit structure and function of RNA polymerase. The mechanisms for unstable initiation of gene expression will be studied by genetic mapping techniques and factors affecting the formation and excision of tandem chromosomal duplications will be analyzed. Studies will be made to determine if DNA insertions into the bacterial chromosome have effects on the formation of transducing DNA fragments and the basis for the specificity of interaction between the phage encapsulating mechanism and the substrate DNA will be analyzed.