106 



R. MARKHAM 



TABLE IV 

 Grams Amino Acid per 100 Gm. Protein » 



3' A, top component; B, bottom component (Fraser and Cosentino, 1957); C, whole 

 virus (Roberts and Ramasarma, 1952) of type strain. 



F. The Nucleic Acid 



The ribonucleic acid of the turnip yellow mosaic virus constitutes some 

 37 % of the total weight (as the free acid) and thus has a "molecular weight" 

 equivalent to 1,850,000. Attempts have been made to estimate the actual 

 molecular weight of the nucleic acid by various methods, but none are 

 unequivocal. Certainly the estimates made by the analytical estimation of 

 end groups by Markham and J. D. Smith (1952c) are obviously in error, 

 probably owing to contamination with plant ribonuclease. 



The nucleotide composition of the nucleic acid is of mterest because of its 

 unusual distribution of bases (Markham and J. D. Smith, 1950). The bases 

 are: adenine, 23; guanine, 17; cytosine, 38; and uracil, 22 residues per 100 

 residues. This composition is so unusual that it has defied all the attempts to 

 fit it to any of the proposed schemes of ribonucleic acid structure. 



The sugar was first shown to be ribose by chromatographic methods, and 

 later by using ribonuclease (Markham "and Smith, 1952a). This nucleic acid 

 was in fact used as substrate in many of the experiments involved in the 

 study of ribonuclease action. 



