32 



THE BIOSYNTHESIS OF PROTEINS 



The sequence of the bases, adenine, guanine, cytosine and uracil along 

 the phosphate-carbohydrate backbone is not known for any RNA. There is 

 evidence, nevertheless, that it is diff-^rent in the RNA of different viruses 

 (Reddi, 1959). In contrast with the data on DNA composition, no rule or 

 regularities have been found for virus RNA, although for the mixture 



Fig. 16. Molecular model of a two-strand helix of DNA (Feughelman 



et al, 1955). 



of RNAs extracted from animal or plant cells and from bacteria, the 

 number of 6-keto groups was found to be close to the number of 6-amino 

 groups. 



X-ray studies on tobacco mosaic virus indicate that the virus RNA is 

 made of a single polynucleotide chain of about 6000 nucleotides which rests 

 in a spiral grove formed in the regularly packed protein units. This RNA 



