BIOLOGICAL ROLE OF PENTOSE NUCLEIC ACIDS 519 



PNA play the same essential role in protein synthesis by living cells? This 

 is the question we have recently been trying to answer (Brachet^^O using 

 again ribonuclease as an analytical tool. Experiments by Kaufmann and 

 Das^^" have shown that ribonuclease penetrates into living root-tip cells, 

 where the enzyme induces various mitotic abnormalities. Ribonuclease, as 

 shown by our co-worker Ledoux,"*"^ also inhibits quickly and powerfully 

 the cleavage of Amphibian eggs. 



The main results obtained from onion roots (Brachet^^) are as follows: 

 ribonuclease quickly inhibits the incorporation of labeled amino acids into 

 the proteins of the living cells without affecting at all the respiration of the 

 root tips. The enzyme first stimulates, then inhibits, the incorporation of 

 labeled adenine into PNA. The incorporation of labeled adenine in DNA 

 is, on the contrary, immediately inhibited. The total amount of PNA drops 

 by some 20 % in the enzyme treated roots, while free nucleotides accumu- 

 late. Phosphorylations seem to be affected by ribonuclease, since its action 

 leads to a drop in the inorganic phosphate and an increase in the ATP 

 contents. 



These results clearly show that PNA also plays a very important part 

 in the incorporation of labelled amino acids into the proteins of living, 

 normally respiring cells. The fact that a large proportion of PNA remains 

 intact speaks rather in favor of a template mechanism, in which partially 

 degraded PNA would prove useless. The simultaneous accumulation of 

 ATP points toward an imperfect utilization of this substance and would 

 fit in with Dounce's^*^ hypothesis of a phosphorylated PNA as the active 

 template. 



It is obvious, from the unusual length of this addendum, that impressive 

 progress has been made during the past few months; it is to be expected 

 that many more spectacular advances will be made in the near future. We 

 have now the possibility of studying the role of PNA in living cells as well 

 as in relatively simple systems. The problem of the role of PNA in protein 

 synthesis is no longer cytochemical; it has finally become a biochemical one. 

 Very soon, PNA will cease to be a mysterious "deus ex machina" and we 

 will really begin to understand how it works. 



The author wishes to thank Professor J. N. Davidson, Professor R. Jeener, and 

 Professor H. Chantrenne for placing manuscripts of papers in press at his disposal 

 and for invaluable help in improving the text of the present review. 



"1 J. Brachet, Nature 174, 876 (1954). 



2" B. P. Kaufmann and N. K. Das, Carnegie Inst. Wash. Year Book 52, 238 (1953). 



273 L. Ledoux, Biochim. et Biophys. Acta 15, 143 (1954). 



"4 L. Ledoux, J. Le Clerc, and F. Vanderhaeghe, Nature 174, 793 (1954). 



