The Biochemistry of Lysogeny 



47 



In Fig. 7, a typical experiment on the relative changes in RNA and 

 DNA and acid-soluble fragments on glucose starvation of E. coli K 12 

 W-6 are shown. Since the probable error of cell counting is 10'y , 

 the changes cannot be considered as significant except for the decrease 

 in RNA and the increase in dilute-acid-soluble fragments after 4 hours 

 of starvation. The stability of the nucleic acid levels on glucose star- 

 vation may be related in this mutant to the presence of excess methio- 

 nine in the medium or to some metabolic products resulting from its 

 genetic deficiency. 



20 



1:10 in 

 C 10 



S 



10 



Hi Acid wash 



ElRNAP 



EZ3DNAP 



1L 



^JA 



n 



Hours of starvation 



Fig. 7. Relative changes in nucleic acid content on glucose starvation of E. coli 



K 12 W-6. 



In Fig. 8, the results of a typical experiment on methionine starvation 

 of E. coli K 12 W-6 are summarized. There was no detectable change 

 in the number of viable cells throughout the 6 hours of starvation. 

 There was about a 30% increase, however, in the turbidity of the cell 

 suspensions, indicating either an increase in cell size or a change in the 

 light-scattering property of the starved cells. The RNA, DNA, and 

 acid-soluble fragments are represented in the figure as changes from 

 the values found when the organisms were harvested from logarithmic 

 growth phase and resuspended in the medium lacking methionine. No 

 unequivocal interpretation can be offered for the 17% increase in total 

 DNA during the first hour of starvation. It may represent increased 

 DNA per cell, or it may be the result of a correspondingly increased 

 cellular population, from the utilization of residual intracellular methi- 

 onine, during the first 15 to 20 minutes of incubation in the me- 

 thionine-deficient medium. The magnitude of the increase in DNA is 

 not quite double the magnitude of the error of cell counting under the 

 best conditions, and, unfortunately, cell counting during the fust 30 



