CHEMICAL PATHWAYS 



119 



bound individually to specific ribonucleic acids (transfer RNA) and it is 

 very tempting to consider these as the adaptors which will carry the 

 activated amino acids to the template and locate them at their right position 

 according to Crick's scheme. This hypothetical mechanism (Hoagland 

 et al., 1959) is depicted on Fig. 31. The template carrying specific informa- 

 tion is supposed to be microsomal RNA. So far, experimentation has been 

 unable to attribute a clear function to the RNA of the ribosome, which 

 constitutes some 80 per cent of cellular or bacterial RNA. But it has been 

 recognized a long time ago that the intensity of protein synthesis is related 



E3(AMP-aa3) + 



Fig. 31. A hypothetical scheme for the interaction of microsomal RNA 

 and transfer RNAs with amino acids attached (Hoagland etal., 1959). 



to the amount of RNA, and essentially of ribosome RNA (Brachet, 1941). 

 Nascent polypeptides, in liver and bacteria, are found in association with 

 the ribosomes. The assumption that ribosome RNA is the template or is 

 part of it, is therefore reasonable. The fact that modifications of soluble 

 RNA can stop protein synthesis is quite compatible with the above 

 scheme. 



There is one difficulty, in this hypothetical template process, it is the 

 size of soluble RNA. A sequence of three to five nucleotides should be 

 sufficient to code for an amino acid. If we add to it the terminal cytidyl- 

 cytidyl-adenosine sequence to which the amino acid is bound, this makes 



I 



