34. THE RIBONUCLEIC ACIDS OF VIRUSES 



253 



be due, therefore, to the presence of RNA at this radius. 41 The density 

 minimum at 40 A. in RNA-free virus protein is no broader or deeper than 

 other minima in the radial density distribution for the protein moiety. It 

 seems, therefore, that the RNA must be fitted in a very compact way into 

 the structure of the virus protein. From Fig. I, 42 it may be seen, further, 

 that the virus particle has a hollow core of radius about 20 A. The RNA is 

 deeply embedded in the protein, following the protein helix in the form of 

 a single molecular chain with the same pitch of 23 A. and a diameter of 

 80 A. (Fig. 2 43 ). There are about 50 bases per turn of helix, aligned parallel 

 to the longitudinal axis of the virus particle. The length of the RNA helix, 

 calculated from its diameter and pitch, and from the whole length of the 



MAXIMUM RADIUS 



RADIUS of HOLE 

 NUCLEIC ACID 



Fig. 1. Schematic representation of a short length of the TMV particle cut in 

 half along a plane through the particle axis, showing the helical arrangement of pro- 

 tein subunits, the helical groove with its accompanying helical ridge, and the hollow 

 axial core. [R. E. Franklin, A. Klug, and K. C. Holmes, in "The Nature of Viruses" 

 (G. E. W. Wolstenholme and E. C. P. Miller, eds.), p. 39. Churchill, London, 1957.] 



41 R. E. Franklin, Nature 177, 929 (1956). 



42 R. E. Franklin, A. Klug, and K. C. Holmes, in "The Nature of Viruses" (G. E. 

 W. Wolstenholme and E. C. P. Miller, eds.), p. 39. Churchill, London, 1957. 



43 W. Ginoza, Nature 181, 958 (1958). 



