CELL DIVISION AND PROTEIN SYNTHESIS 543 



have found it to be around 60 min. before division in the logarithmic cell 

 growing in proteose-peptone plus 0-4% liver extract. 



We have further analyzed this effect by exposing the cells (medium as 

 before) to 16 mM/)-FPhe for only 20 min. After that time the inhibitor is 

 removed by three washings with fresh growth medium, using the hand 

 centrifuge. The control is similarly treated in a parallel tube. The results 

 are shown in Fig. 5. In this case we have only delay, never block of division. 

 The delays are plotted against the time of immersion into the inhibitor. 

 Curve I represents the delay of division i (lengthening of time interval 

 from EH to division i). Curve II measures the delay of division 2 in terms 

 of extended intervals between divisions i and 2. Several experiments are 

 combined but little attempt has been made of keeping them apart because 



60 120 



Minutes after E H. 



180 



Fig. 5. Delay of synchronous division in proteose-ptptone by 16 niM p-FPhe 

 for 20 min. The abscissa is the time when the exposure is initiated. Cnric I: Delay 

 of division i. Curve II: Delay of division 2 (lengthening of time interval between 

 divisions i and 2). 



both the svnchronizations and the responses to the analogue are so nicelv 

 reproducible. Only the arrows which show the times for maximal division i 

 and 2 separate between experiments. The results confirm those of Fig. 4 

 in showing that there is a critical time about 44 min. before division i, 

 and 50 min. before division 2 when the response to/)-FPhe drops sharply. 

 The new information conveyed by Fig. 5 is that the reaction to a standard 

 treatment with the analogue increases (cur\e I) from EH to reach a 

 maximum value (at t^^ min.) just before the drop in advance of division i. 

 Further (curve II), that this cvclic variation repeats itself between divisions 

 I and 2 and even extends back in time (left part of curve II) to before 

 division i. Thus, 20 min. of exposure to the amino acid analogue, made 

 before division i delays the preparation, not of this immediate division, 

 but of the next one. However, this delay of division 2 is only slight and of 

 the same order as the exposure time (20 min.) to the analogue. Curve I 



