X. TMV STUDIES IN GENETIC CODING 487 



(see Fig. 3). The amino acid sequence of no other polypeptide of similar 

 size has been established at two laboratories, and thus with a similar 

 degree of certainty. Some of the particular features of this structure have 

 previously been mentioned in connection with the functional aspects of 

 the protein. 



III. TMV-RNA 



The amount of RNA in TMV and most other simple RNA viruses 

 corresponds to a molecular weight of about 2 X 10". In the case of TMV 

 the evidence from X-ray diffraction and electron microscopic analyses 

 suggests strongly that each virus particle actually contains but one 

 molecule of RNA of that molecular weight (Franklin et al., 1957; Hart 

 1958). The RNA occurs as a single unbranched chain of about 6400 

 nucleotides running through the rod at a diameter of 80 A and of the 

 same helical pitch as the protein units to which it is probably bound by 

 3 phosphates per subunit. The length of the RNA thus limits the length 

 of the stable virus rod to 6400/3 protein units, or a particle weight of 

 (2130 X 17,800) + (2 X lO'') = 40 X lO''. It should be noted that the 

 helical path through which passes the RNA within the rod does not 

 allow for any contact or interaction of bases (Ginoza, 1958) as indicated 

 by the hypcrchromed state of the RNA in situ (Bonhoeffer and Schach- 

 man, 1960). 



A number of different conditions which disaggregate the protein units 

 have been employed for the separation and isolation of the RNA. Since 

 the RNA is more sensitive to H^ and OH" ions than the protein, only 

 those methods which proceed near neutrality yield biologically fully 

 active RNA. Detergents (Fraenkel-Conrat and Williams, 1955; Fraenkel- 

 Conrat et al., 1957) and phenol treatment (Gierer and Schramm, 1956) 

 fulfill this requirement, and the phenol method has found particularly 

 wide acceptance because of its simplicity and reliability. 



TMV-RNA, as isolated in such manner, appears to contain less than 

 1% of protein, and no other known contaminants. If the acidic clay 

 bentonite is added in the isolation of the RNA, the resultant prepara- 

 tion contains less than 0.05% of protein, and from its markedly increased 

 stability properties it is concluded that nucleases probably represent the 

 main proteinaceous contaminant of non-bentonite-treated RNA prepa- 

 rations (Fraenkel-Conrat et al., 1961; Singer and Fraenkel-Conrat, 

 1961). 



Sedimentation analyses of the RNA show a main component of about 

 30S, which corresponds to the expected molecular weight of 2 X lO*' for 

 the complete RNA moiety of one virus particle (Gierer, 1958a,b; Boedt- 

 ker, 1959). However, from 20-50% of the material shows a broad 



