34. THE RIBONUCLEIC ACIDS OF VIRUSES 299 



whereas low molecular weight RNA remains in solution and can be pre- 

 cipitated only with alcohol. 



Colter et al. 143 - m - m prepared RNA from Ehrlich ascites carcinoma cells 

 by phenol extraction. This was not homogeneous in that ' 2 ^ of the material 

 exhibited a sedimentation constant of less than 3 S, and the remaining RNA 

 sedimented into two components with sedimentation constants of 32 and 

 15 S. A comparison was made between RNA extracted from noninfected 

 Ehrlich carcinoma cells with that from cells infected with Mengo and West 

 Nile viruses. A similar comparison was made between RNA extracted from 

 noninfected hamster brains and brains from hamsters infected with polio- 

 virus. In all cases, there was no qualitative difference in the ultracentrifuge 

 patterns of RNA from infected and noninfected material. The RNA com- 

 ponents having sedimentation constants of 15 and 32 S could be quantita- 

 tively precipitated with 1 M NaCl and the infectivity was always recovered 

 quantitatively in the precipitate. The infective component probably sedi- 

 mented with the 32 S component. 



Studies on nucleic acid isolated from chicken embryos infected with EEE 

 virus led to similar results. 166 Three components could be identified in the 

 ultracentrifuge. Two high molecular weight components sedimented with 

 s 2 o approximately 31 and 19 S and the cellular DNA sedimented with 

 S20 ^ 12 S when this was present in the preparation. Also, in this case, it 

 is most likely that the infectivity sediments with the 31 S component. 



Strohmaier and Mussgay 179 centrifuged infectious RNA from foot and 

 mouth disease virus in a density gradient (D 2 0-H 2 0), and found a value of 

 37 S for the infectious component. 



In general, it is possible to determine the molecular weight of infectious 

 RNA by measurements of sedimentation and viscosity [see Section III, c, 

 (1)]. However, virus RNA is only an insignificant fraction of the total RNA 

 extracted from virus-infected cells and, therefore, it is not possible to de- 

 termine the molecular weight of virus RNA from measurements of sedi- 

 mentation and viscosity on such extracts since the viscosity of virus RNA 

 cannot be determined in the presence of an overwhelming higher concen- 

 tration of cellular RNA. However, the molecular weight may be estimated 

 from the sedimentation constant alone by employing the empirical relation- 

 ship between sedimentation constant s and molecular weight m determined 

 for TMV-RNA. 68 



m = 1100 s 2 - 2 (9) 



This formula can be applied, generally, only under two conditions: (1) 



178 R. A. Brown, M. C. Davies, J. S. Colter, J. B. Logan, and D. Kritchevsky, Proc. 

 Natl. Acad. Sci. U.S. 43, 857 (1957). 



179 K. Strohmaier and M. Mussgay, Z. Naturforsch. 14b, 171 (1959). 



