The Biochemistry of Lysogeny 49 



Electron-microscope photographs of this starved mutant revealed 

 enlarged, often misshapen, cells loaded with electron-dense material. 



The increase in nucleic acid material on methionine starvation in 

 E. coli K 12 W-6 parallels similar changes in microorganisms when they 

 are exposed to drastic shocks. Mitchell reported an increase in the 

 free nucleotide content of bacteria after the "initial attachment of 

 penicillin to growing cells." 10 Park and Johnson showed that in 

 Staphylococcus aureus in presence of 0.1 of a unit of penicillin per 

 milliliter there is about a 40^ increase in RNA in 65 minutes with 

 no concurrent change in the cell count. 11 Kelner has noted that there 

 is a marked increase in RNA in E. coli B/r following a dose of ultra- 

 violet irradiation which prevents 90 c /c of the organisms from giving 

 rise to visible colonies. 12 



However, the large increase solely in RNA content, upon starvation, 

 seems to be unique to this auxotroph. The appropriate autotrophs 

 of E. coli Ki 2 when starved of histidine, tryptophane, and leucine, 

 respectively, yielded values similar to those obtained upon glucose 

 starvation of E. coli \\]> W-6. 



We also studied a methionine-requiring mutant of the W strain of 

 E. coli which was kindly supplied, as were those listed above, by 

 Dr. Bernard Davis. The W strain is lysogenic but, unlike the K i2 

 strain, the frequency of the occurrence of the phenomenon in a given 

 population cannot be increased by radiations or other inducing agents. 

 The methionine-requiring auxotroph of the W strain, W 122-33, ap- 

 pears to have a genetic block analogous to that of E. coli K 12 W-6, as 

 far as this can be determined by the probably not-too-discriminating 

 technique of the determination of accumulated metabolic precursors. 

 This putatively analogous mutant of the W strain did not accumulate 

 nucleic acid material on methionine starvation. 



The unique ability of E. coli W-6 to synthesize RNA independently 

 of DNA and of protein (for there was no increase in total protein 

 content) may be put to use to study the relations among the syntheses 

 of these three entities, but here we are concerned only in what this 

 mutant may have contributed to an understanding of inaptitude. The 

 two types of starvation, glucose and methionine, have parallel effects 

 on inaptitude, but, by rare chance, they have divergent effects on the 

 nucleic acid content of the starved cell. Intracellular screening by 

 nucleic acids or fragments thus appears to be an unlikely mechanism 

 for inaptitude. 



We are thus back where we started. We learned a bit about nucleic 

 acid metabolism, but apart from the essentially negative contribution 



