Six analogues of amino acids killed corresponding auxotrophs of Escherichia coli . With all but one analogue, protein synthesis was required for lethality.

Methioninp auxotrophs of strains derived from Escherichia coli 15 lose their colony-forming ability when deprived of this amino acid. Late addition of methionine to liquid cultures did not restore plating efficiency but permitted growth of surviving cells. This phenomenon, termed methionineless death (mid), was not observed with methionine auxotrophs of E. coli strains B, W, or K12, nor was a similar amino acidless death observed with corresponding auxotrophs of E. coli 15 for arginine, tryptophan, proline, isoleucine, and leucine. Mid was not dependent upon the genetic site determining methionine auxotrophy, nor did it affect the decarboxylation of methionine or the stability of methionyl-transfer ribonucleic acid synthetase activity of starved cells. Death was not altered by the presence of spermine or spermidine but was abolished by the methionine analogue, a-methylmethionine. Simultaneous starvation of another amino acid in a multiple auxotroph also significantly reduced mid, suggesting a possible role of protein synthesis. The onset of mid is correlated with a lower net increase of deoxyribonucleic acid. 100 AM and the missing growth requirements were added. The incubation was continued, and at various 1168