The objective of this project is to make a detailed analysis of the inducible, high-level mistranslation seen when bacterial or mammalian cells are starved for certain amino acids. This mistranslation is easily observed on two-dimensional gel electropherograms. Since the phenomenon seems identical in both bacterial and mammalian systems, we shall use Escherichia coli as a model. We plan to characterize more fully the conditions under which this mistranslation occurs by 1) performing the experiments in isogenic strains 2) use of auxotrophs and amino-acid analogs 3) use of the temperature sensitive mutations of the asparaginyl-tRNA synthetase (asnS) and the histidyl-tRNA synthetase (hisS). We shall also determine if other mutations known to affect translational fidelity (rpsD equals ramA, rpsL equals strA, relA) alter the response of the cell to the starvation. Using E. coli infected with the small RNA virus, MS2, we will examine the exact nature of the amino acid substitution and its specificity. We will purify mistranslated viral proteins and do amino acid and peptide analysis. The stability of mistranslated bacterial proteins will be examined in wild-type strains and strains defective in specific proteolyzing systems.