8(iO HICHARI) SCinVEKT AND JOHN BISIIOI' 



separation (Berg ami Lajjjerkvist, 1962). The results shown in Table I 

 indicate a remarkable degree of heterogeneity in T-RNA, considering 

 that only the first few nucleotides have been analyzed. These results 

 indicate nuuli gi eater differences in various T-RNA types than would 

 be expected if the only differences were those in the code, which is 

 expected to be a trinucleotide or in that size range. It is of interest to 



emphasize that even the molecules which have pCpCpA as their 



sixth, fifth, and fourth residues (sequences 6 and 10, Table I) are inactive 



TABLE I 



Terminal Nucleotide Sequences of Amino Acid-Acceptor RNA" 



Per cent of RNA chains 



Seciuence^ having .sequence shown 



1. RNA pGpApCpCpA 6-8 



2. pGpCpA 25-30 



3. pGpCpU 6 



4. pGpUpA 3 



5. pGpCpCpU 2 



6. — pGpCpCpA 4 



7. pGpApG 4 



8, pGpCp(UpC)pA 7-9 



9. pGpCp/UpCpOp 7-12 



10. pGpApCpCpCpA 4-9 



11. pGpUp(CpCpU)pG 5 



" Taken from Berg and Lagerkvist (1962). 



* All the sequences terminate in pCpCpA as shown in the first Hne. These have 



been omitted for simj)licity in the lower lines. The exact sequences shown in parentheses 

 are not known. 



in forming amino acyl-RNA compounds, when the terminal three 



nucleotides are removed. The complete sequence, in this case 



pCpCpApCpCpA, is required for activity. Using similar techniques 

 combined with periodate oxidation of chains not protected by attached 

 amino acid, it was also shown by these authors that the chains for 

 isoleucyl-RNA and leucyl-RNA were different. However, the leucyl- 

 RNA contained sequence 2 (Table I) which is present in 25-30% of 

 chains and undoubtedly is not specific for leucyl-RNA. Differences in 

 T-RNA fractions eluted from Brushite columns were found by Cantoni 

 (1962). There was a progressive change in C plus A content and in the 

 "odd" base content of various fractions. Although the purine to pyrimi- 

 dine ration was 1 in all fractions, the A to U plus pseudo-U ratio 

 departed significantly from unity in some fractions. Thus the resem- 

 blance to T^NA noted by some authors does not appear in all fi-actions. 



