VI. RNA AND CODING PROBLEMS 283 



ber of amino acids. The ratio of three has a rather solid basis in terms 

 of both the theoretical and experimental approach (see below). At the 

 risk of publishing the score in the middle of the ball game, I have 

 compiled the presently available "genetic code" for 17 amino acids in 

 Table I. It should be noted that the sequential order of the nucleotides 



TABLE I 

 Genetic Code for Polymerization of 17 Amino Acids" 



Amino acid Triplet code letter'' 



Ahinine lU IC IG 



Arginine lUlClG 



Cysteine 2U IG 



Glutamic acid lU IC IG 



Glycine lU 2G 



Histidine lU lA IC 



Isoleucine 2U lA 



Leucine 2U IC, 2U IG 



Lysine lU 2A 



Methionine UG' 



Phenylalanine UUU 



ProUne lU 2C, [CCC] 



Serine 2U IC, UGC, 2U IG 



Threonine lU 2C 



Tryptophan lU 2G 



Tjrosine 2U lA 



Valine 2U IG 



° Compiled from the data in Lengyel et al. (1961, 1962), Nirenberg and Matthaei 

 (1961), Martin et al. (1962), Speyer et al. (1962). 

 * Sequential order unspecified. 

 <= Not further specified (Martin el al, 1962). 



in any triplet (with the obvious exception of UUU = phenylalanine) 

 cannot as yet be specified. In addition, the fact that more than one 

 triplet can specify a single amino acid shows that the code is degen- 

 erate; that is, more than one coding unit can specify the insertion of a 

 single amino acid. Thus, it should be clear that the use of enriched 

 polyuridylic acid sequences as a "handle" probably weights the present 

 code toward this nucleotide. A number of other triplets, absent in uridylic 

 acid, could be equally specific for some of the amino acids listed. 



Wood and Berg (1962) have succeeded in demonstrating a significant 

 amino acid activating effect by enzymatically synthesized RNA w'ith a 

 system consisting in ribosomes plus a soluble fraction that had been 

 virtually freed of DNA. In particular, the addition of T2 phage DNA, 

 the four ribonucleoside triphosphates and RNA polymerase resulted in 

 a 4-fold increase in rate of reaction and a 20-foId increase in extent of 



