364 



MAHLON B. HOAGLAND 



S + [oZ] 



ATP 



activation 

 PP 



ATP+ 2CTP< 



RNA 



E(AMP-aa ) 



V 



preparation of RNA end 

 RNA-CCA^ ^3PP 



attachment to RNA 



AMP+E 



ribosome 



transfer to ribosomes ~~^ G T P 

 RNA- CCA 



ribosome protein*) 



endoplasmic membrane 



removal of finished protein 



ribosome 



membrane + protein* 



A 



Fig. 1. Steps in protein synthesis. 



scheme is based has been derived from in vitro cell-free systems, certain 

 basic observations antedated the advent of active cell-free systems and 

 should be mentioned briefly. The pioneering studies of Schoenheimer 67 and 

 Rittenberg 68 indicated that isotopic protein precursors were rapidly in- 

 corporated into protein in vivo and pointed the way to the later use of C 14 - 

 and S 35 -labeled amino acids to study protein synthesis in slices, minces, 

 and dispersed cell systems. Extensive studies were first undertaken by 

 Zamecnik and his associates in rat liver, tumor cells, embryonic tissue, and 

 silk glands, 69 " 72 by Borsook and his colleagues using bone marrow cells, 73 



67 R. Schoenheimer, "The Dynamic State of Body Constituents." Harvard Univ. 

 Press, Cambridge, Mass., 1942. 



68 D. Rittenberg, Harvey Lectures 44, 200 (1950). 



69 I. D. Frantz, Jr., R. B. Loftfield, and W. W. Miller, Science 106, 544 (1947). 



70 P. C. Zamecnik, I. D. Frantz, Jr., R. B. Loftfield, and M. L. Stephenson, J. Biol. 

 Chem. 175, 299 (1948). 



71 I. D. Frantz, Jr., P. C. Zamecnik, J. W. Reece, and M. L. Stephenson, J. Biol. 

 Chem. 174, 773 (1948). 



72 P. C. Zamecnik, R. B. Loftfield, M. L. Stephenson, and C. M. Williams, Science 

 109, 624 (1949). 



73 H. Borsook, C. L. Deasy, A. J. Haagen-Smit, G. Keighley, and P. H. Lowy, J. 

 Biol. Chem. 186, 297 (1950). 



