38. BIOSYNTHESIS OF PROTEINS IN BACTERIAL CELLS 439 



to a suspension of an auxotroph previously starved of its essential amino 

 acid, the missing amino acid is added, normal growth is restored and RXA 

 synthesis is proportional to the amount of the amino acid added. If, to the 

 same suspension, the amino acid is added in the presence of chlorampheni- 

 col, RXA synthesis is restored equally well, although this amino acid can- 

 not be incorporated into protein. 27, 28, 163 In addition, restoration of RXA 

 synthesis in the presence of chloramphenicol can be observed on addition 

 of traces of the essential amino acid. 28 



This experiment shows (1) that amino acids play a role as such (in the 

 "free" or "activated" form) during the synthesis of RNA; (2) that amino 

 acids function as catalysts in the synthesis of RX'A; calculation shows that 

 for each molecule of essential amino acid added after starvation and in the 

 presence of chloramphenicol, at least ten nucleotides are incorporated into 

 RNA. 28 



These results are considered to indicate that bacteria, and possibly all 

 cells, contain common precursors for protein and RXA. These precursors 

 could consist of complementary associations between amino acids and 

 specific oligonucleotides. In order for the oligonucleotides to be distributed at 

 the surface of a specific template in the right sequence, all the amino acids 

 to which these nucleotides are attached should have to be distributed also 

 according to a complementary sequence. The lack of an amino acid would 

 result in an interruption in the sequence of nucleotides. On the other hand 

 the mechanism for joining the nucleotide subunits would function even if 

 the complementary amino acids were not bound by peptide linkages, provid- 

 ing all are present in the right sequence at the surface of the template. 



Other workers have interpreted the necessity of the amino acids for 

 RXA synthesis in a completely different manner, assuming the formation 

 of a specific protein, the synthesis of which would be insensitive to chlor- 

 amphenicol, but whose presence would be required for RNA synthesis. 164 

 The difficulties associated with this interpretation have already been dis- 

 cussed elsewhere. 28 



It has also been suggested that free amino acids could be involved in the 

 recycling of the sRX'A after it has undergone specific molecular splitting 

 during the adaptation of the amino acids on the template. 165 This inter- 

 pretation could not account, however, for the mechanism of RXA synthesis 

 during chloramphenicol inhibition, since most of the chloramphenicol RXA 

 — the formation of which depends on the presence of free amino acids — 

 exists in a particulate form (15 S). 



163 M. Yeas and G. Brawerman, Arch. Biochem. Biophys. 68, 118 (1957). 



164 A. I. Aronson and S. Spiegelman, Biochim. et Biophys. Acta 29, 214 (1958). 



165 F. H. C. Crick, Symposia Soc. Exptl. Biol. 12, 138 (1958). 



