S. SPIEGELMAN AND A. M. CAMPBELL 



be performed with intact cells, the distance between the data 

 and the conclusions derived fr ^m them is too great for certainty. 

 Definitive identification of the chemical nature and the mode of 

 action of the template is not likely until the latter has been phys- 

 ically isolated in a functional state. In vitro performance of its 

 function by the isolated enzyme-forming system may be sug- 

 gesting the impossible, since it demands even more than that 

 which has already been accomplished in the case of transfor- 

 mation in the bacteria. In the latter, genetically competent 

 material has been separated from other cell c 3mponents. How- 

 ever, the transforming principles have been asked to function 

 only after reinsertion into an intact living organism. 



Nevertheless, that the ideal in vitro situation may be attain- 

 able in the not too distant future is prophetically foreshadowed 

 by the striking successes which have recently been recorded with 

 subcellular fractions. Many of these deal primarily with in- 

 corporations studies. To this extent it is uncertain that they 

 necessarily represent model systems which will permit the 

 further dissection of the protein-synthesizing mechanism. The 

 data must therefore be interpreted with caution, but their 

 uniqueness and potential value command consideration. 



Zamecnik and Keller (104) succeeded in preparing a mi- 

 crosome fraction which actively incorporates amino acids when 

 supplemented with some component of the supernate and an 

 ATP-generating system. Subsequent work on the supernate 

 fraction by Keller and Zamecnik (42) indicated the presence of 

 an enzyme which generated guanosine-triphosphate, a deriva- 

 tive of which functions in the insertion of the amino acids into 

 peptide linkage. The work of Hoagland (37) and DeMoss and 

 Novelli (22) strongly suggests that polyphosphate derivatives of 

 nucleotides activate amino acids prior to their incorporation. 



Lester (48) and Beljanski (6) examined the ability of 

 lysozyme-treated preparations of Bacillus megaterium to incor- 

 porate amino acids labeled amino acids. Both authors found 

 that treatment with RNase abolished this ability, whereas ex- 

 posure to DNase was stimulatory. 



154 



