BIOLOGICAL ROLE OF PENTOSE NUCLEIC ACIDS 511 



folds to form a three-dimensional globular protein molecule. The main 

 function of PNA would be to maintain the protein template in the ex- 

 panded state of a film. 



Caldwell and Hinshelwood^"* point out many analogies between auto- 

 synthesis and the growth of crystals. They believe that nucleic acids, by a 

 process akin to crystallization, impose a definite order on the arrangement 

 of the amino acids. A converse mechanism would control synthesis of 

 specific nucleic acids by the newly built protein. Such a theory requires 

 the presence in the cell of a large number of self-duplicating nucleoproteins, 

 of which the protein part would have specific enzymic activity. Further- 

 more, if we admit that PNA acts as an organizer or template for protein 

 synthesis, it follows that increased PNA will lead to increase in protein 

 production. 



While there is no evidence to prove conclusively the existence of a tem- 

 plate mechanism, many experimental results fit in well with this hypothe- 

 sis. These include Gale and Folkes'^^ observation that certain antibiotics, 

 as already found by Levy et al.^^ and Miura et al.^^'^^ for cobaltous ions 

 and usnic acid, inhibit protein synthesis while the rate of PNA formation 

 is increased. The antibiotics presumably act on the splitting off of the 

 nucleoprotein complex. As Hammarsten-"^ points out, these experiments 

 emphasize that protein synthesis is secondary to PNA synthesis, and they 

 suggest that nucleoprotein synthesis not only precedes protein synthesis 

 but is even necessary for the latter. It has been demonstrated that in 

 pancreatic tissue stimulated to enzyme production by pilocarpine (Hokin,^''^ 

 De Deken-Grenson,2°^ 209) ^j^,^ jj^ ^j^g secreting oviduct of laying hens 



(Grenson^^"), the synthesis of proteins is not linked to the rate of uptake 

 of P^2 into PNA. These observations are in better agreement with the 

 template hypothesis than with any other. As Hokin^"^ points out, it would 

 seem that PNA plays a part during the rearrangement and movement of 

 enzymes during secretion. Nucleoproteins or PNA might act as a specific 

 framework onto which enzyme systems could be organized and which 

 could direct the synthesis of more PNA. Such a view is consistent with 

 the results of Daly and Mirsky,^'^ indicating that the total protein content 

 of the pancreas remains constant during the cycle of secretion and synthe- 

 sis: when enzyme secretion takes place, rapid synthesis of a precursor 

 protein would occur, which would be followed by gradual transformation 

 into the characteristic pancreatic enzymes. 



^"^ E. Hammarsten, Ciba Conf. on Isotopes in Biochem., London p. 203 (1951). 



207 L. E. Hokin, Biochim. et Biophys. Acta 8, 225 (1952). 



208 M. De Deken-Grenson, Biochim. et Biophys. Acta 10, 480 (1953). 



209 M. De Deken-Grenson, Biochim. et Biophys. Acta 12, 560, 1953. 

 2'o M. Grenson, Biochim. et Biophys. Acta 9, 102 (1952). 



"' M. M. Daly and A. E. Mirsky, J. Gen. Physiol. 36, 243 (1952). 



