34 



RIBONUCLEIC ACIDS AND PROTEIN SYNTHESIS 



ment decreases the basophilia of sea urchin eggs, and from the 

 discovery by Kaufmann and Das (1955) and by Ledoux and Baltus 

 (1954) that ribonuclease induces mitotic abnormalities in onion 

 roots and in ascites tumor cells, we decided to study the biochemical 

 effects of ribonuclease on various cells. The main results are summa- 

 rized below. 



In onion root-tips (Brachet, 1954, 1955b, 1956a), crystalline 

 ribonuclease at 1 mg/ml concentration produces a 50% inhibition 

 of amino acid incorporation into the proteins within 1 hour; the 

 inhibition becomes almost complete (90%) after a 3-h treatment. 



7 h 



Fig. 13. Effects of ribonuclease and RNA on growth rate of onion roots. RNase: 

 addition of Armour ribonuclease 1 mg/ml; HoO: washed with distilled water; 

 RNA: addition of ribonucleic acid (1%). Experiments were performed on 

 the same onion cut into two parts. All solutions were aerated (Brachet, 1955b). 



These observations were made both by conventional biochemical 

 techniques and by autoradiography. Figs. 1 1 and 12 (p. 33) illustrate 

 the type of results obtained by the autoradiography method, in the 

 case of phenylalanine incorporation. The inhibition of the incor- 

 poration of the amino acids into proteins is faster and stronger than 

 that of the penetration of the free amino acids. This fact indicates 

 that the primary action of ribonuclease is less on cellular perme- 

 ability than on the incorporation reaction itself. 



Furthermore, ribonuclease strongly inhibits the growth of the 



