DAGLEY AND SYKES 



67 



to 



(*) 



to 



ifiB a I P»l _■ ; I ■ *»*..■ .w,.,^..-.,Jl 



GO 



to 



(/) 



Fig. 3. Patterns after 16 minutes' centrifuging at 187,000g for extracts from cells, in 

 stationary-phase glucose mineral salts culture (a); in mid-logarithmic phase after transfer 

 to glucose peptone medium (b) ; in late logarithmic phase in this medium (c) ; after incu- 

 bation with 0.13 M phosphate buffer, pH 7, (d) for 30 minutes and (<?) for 120 minutes. 

 The volume of buffer for resuspension was the same as that of the culture from which the 

 cells were taken. On addition of glucose and peptone to the suspension the cells grew, and 

 pattern (/) was given after 1 hour. 



of magnesium ions with an ultracentrifuge fraction that contains the 40 S 

 component, and, drawing attention to the observation of Webb [19] that bac- 

 teria may synthesize protein but may not divide when there is a deficiency of 

 magnesium, they make the stimulating suggestion that the RNA in this frac- 

 tion is directly concerned with the cell-division process. 



Without further study we cannot conclude that the stability of the 40 S com- 

 ponent in whole cells is determined solely by the concentrations of Mg ++ and 

 other inorganic ions in the medium. Thus it appears that when cells are grown 

 in a rich peptone medium they are less readily depleted of 40 S than when 

 grown in mineral salts; and, in our studies of 3-galactosidase development dur- 

 ing the lag in cell division in a lactose mineral salts medium, we observed a 

 reduction in this component although the magnesium content of the culture 

 was normal. It is therefore possible that other factors concerned with the 

 metabolism of the cell may also control the stabilization or degradation of the 

 40 S macromolecule. 



When a cell-free extract was diluted, or the buffer concentration used in its 



