290 HEINZ SCHUSTER 



On a molar basis, the intact TMV with a molecular weight of 40 X 10 6 

 is about 200 times more active than free RNA. The biological activity of 

 RNA, recombined with protein, is about 60-120 times larger than that of 

 free RNA, or 30-60% of the activity of the original virus. Therefore, the 

 recombination studies suggest that the lower activity of free RNA in solu- 

 tion is probably due to the presence of ribonuclease during inoculation of 

 free RNA and to the sensitivity of free RNA in solution to numerous types 

 of reagents. Thus, the virus protein can be regarded as a stabilizer of the 

 RNA during infection. 



The binding of virus protein to RNA in the reconstitution is not highly 

 specific. This is clearly shown by the fact that synthetic ribonucleotide 

 polymers with molecular weights of 10 4 -10 5 can recombine with native 

 TMV protein into rods of the same apparent width as TMV, but of various 

 length. 142 These rods contain 4-6% ribonucleotide polymers and incuba- 

 tion with ribonuclease caused no appreciable hydrolysis of the nucleic acid 

 component. As is to be expected, such rods possess no biological activity. 



Recombined virus preparations have UV sensitivities which are different 

 from those of normal virus. 85 Many recombined viruses possess the UV 

 sensitivity of their RNA when it is present in a free form, whereas others 

 show sensitivities which lie between that of free RNA and normal virus. 

 The UV sensitivity of recombined virus is never the same as that of normal 

 virus. 



In summary, one might say that the higher biological activity of recom- 

 bined nucleoprotein particles compared with free RNA is most probably 

 due to the stabilizing action of the protein shell which protects the infectious 

 RNA. The viral protein is capable of spontaneous aggregation independent 

 of the presence of other macromolecules. Serum protein, which does not 

 polymerize to form rodlike aggregates, has an inhibitory action on the 

 activity of infectious RNA. 143 Thus, the specificity of the stabilizing action 

 of virus protein probably lies in its ability to form aggregates. 



The nature of the bonding between RNA and protein is not well known. 

 It must be of a rather weak type in view of the relative ease of splitting 

 with phenol at neutral pH and in the cold. Reddi 144 has shown that the 

 UV spectrum of TMV is exactly equal to the sum of the spectra of TMV- 

 RNA + TMV protein after correcting for light-scattering. If the purines 

 and pyrimidines of TMV-RNA are involved in the formation of the nucleo- 

 protein complex in a way to suppress some of the chromophores, one would 

 expect that the UV spectrum of TMV minus the contribution of the spec- 

 trum of the protein part would have a lower absorption maximum than 



142 R. G Hart and J. D. Smith, Nature 178, 739 (1956). 



143 J. S. Colter, Progr. in Med. Virol. 1, 1 (1958). 



144 K. K. Reddi, Biochim. el Biophys. Ada 24, 238 (1957). 



