CELL DIVISION AND PROTEIN SYNTHESIS 54I 



offered at time EH,* regularly dropping precentages when the compound 

 is added later, finally almost no labelling when cells in maximal division i 

 are exposed. This can be repeated with "washed cells" (defined in 

 Section 2). Immersion of washed synchronized cells into a solution of 

 5-fluoro-2-deoxyuridine (5 x 10 -^ m) at EH, thus prior to the addition of 

 the tritiated thymidine reduces to 6-12"',, the average number of tracks 

 over the nucleus which takes the label. It does not significantlv alter the 

 percentage of labelled cells. This is so for all time points studied. The long 

 exposures to this base analogue interfere neither with division i nor with 



OS 



Fk;. 3. The open circles represent log cell number per ml. culnire. The filled 

 circles represent DXA (microbiological assays) and the crosses ( x ) packed cell 

 volume per ml. culture. Increases in cell volume and in DXA go parallel, for the 

 culture and for the average cell. Plotted from Table i in Zeuthen and Scherbauni 



[14]). 



dixision 2. It is not vet proven, but it can be suggested that two syn- 

 chronous divisions can be developed without (^e novo synthesis of DXA 

 after the termination of the temperature shocks. 



4. Studies with amino acid analogues 



The ideas developed in Section 2 have stood the first test with amino 

 acid analogues. The experiments were performed in association with cand. 

 mag. Leif Rasmussen. 



DL-/)-fluorophenylalanine (/)-FPhe) is a strong inhibitor of cell division 



* The time when the last temperature shock ends, as shown by a signal on the 

 control watch. 



