BIOSYNTHESIS OF PROTEIN 645 
acid in preference to its analog®, no further selection occurs after entry of the 
analogue into the internal pool. One wonders whether the amino acids and analogs 
contained in the internal pool have not already been selected by the protein-forming 
templates, but have yet to be linked together in polypeptide strands. 
REFERENCES 
1 R. B. Roperts, P. H. Aperson, D. B. Cowiz, E.T. Botton anv R. J. BRITTEN, Carnegie 
Inst. Wash. Publ. No. 607, 1955. 
2 W.C. SCHNEIDER, J. Biol. Chem., 161 (1954) 295. 
3D. B. CowlE anD B. WALTON, Biochim. Biophys. Acta, 21 (1956) 211. 
4D. B. Cowie anp F. T. McCiure, Biochim. Biophys. Acta, 31 (1959) 236. 
5 E.S. KEMPNER AND D. B. Cowie, Biochim. Biophys. Acta, 42 (1960) 401. 
6 D. B. Cowrsg, unpublished results. 
7G. N. COHEN AND J. Monon, Bacteriol. Rev., 21 (1957) 169. 
8 H. O. HALVORSON AND G. N. CoHEN, Amn. inst. Pasteur, 95 (1958) 73. 
® E. R. STADTMAN, G. N. CoHEN, G. LEBRAS AND H. DE ROBICHON-SZULMAJSTER, J. Biol. Chem., 
236, (1961). 
10 H. E. UMBARGER AND B. Brown, J. Biol. Chem., 233 (1958) 415. 
11H. E. UMBARGER, Science, 123 (1956) 848. 
12, R. E. YATES AND A. B. ParRDEE, J. Biol. Chem., 221 (1956) 757. 
13H. J. STRECKER, J. Biol. Chem., 225 (1957) 825. 
14H. S. MoYED AND B. MaGasanik, J. Am. Chem. Soc., 79 (1957) 4812. 
15 F. LYNEN, Federation Proc., 20 (1961) 544. 
