BIOSYNTHESIS OF PROTEINS 277 



may be compared with a necklace, the nucleic acid corre- 

 sponding with the thread and the fundamental protein 

 molecules with the beads (Fig. 23). 



The work of H. Fraenkel-Conrat and R. C. Williams^^® was 

 a great achievement in the field of virology. These workers 

 succeeded not merely in separating the nucleic acid from 

 the protein components of tobacco mosaic virus, but also in 

 reassembling the virus from these components in a biologi- 

 cally active state. The authors cited lay special stress on the 

 need to retain the separate components absolutely in the 

 native state, if this is to be successful. In particular, it is 

 only by using the unaltered nucleic acid of a virus that 

 positive results can be obtained. When it has been treated 

 with ribonuclease it will no longer serve as material for the 

 assembly of a virus. Equally unsuccessful were attempts to 

 substitute for the RNA of tobacco mosaic virus DNA 

 obtained from the thyroid gland or RNA from the turnip 

 yellows virus. 



The protein component which was separated from the 

 nucleic acid was found by electron microscopy to take the 

 form of discoid particles having a thickness of 50-150 A 

 and a diameter the same as that of the rod of the active virus 

 particle (150 A). In the centre of the disc a hole was found 

 having a diameter of about 40 A (see Fig. 24). 



According to the authors quoted, these discs are in- 

 distinguishable from X-protein. When the active virus is 

 assembled, the protein discs combine with the nucleic acid, 

 which is concentrated in the central cavity and which 

 enables the fimdamental protein molecules to aggregate. As 

 a result of this aggiegation particles are formed which are 

 indistinguishable from the particles of the original virus. 

 They are thus about 3,000 A long. 



The action of detergents on a reconstituted virus produces 

 the same deformation of the particles as in the original virus. 

 The rods are broken up into discs and at the site of the 

 fractures there are seen to be centrally disposed cores which 

 disappear on treatment with ribonuclease, thus showing that 

 they are made up of RNA. 



According to Fraenkel-Conrat and Williams neither the 

 protein nor the nucleic acid by itself shows any sign of 



