288 



HEINZ SCHUSTER 



Uj 



ct 

 *- Uj 



b 01 



10 



20 



30 



40 



50 60 70 60 90 



TIME AFTER INFECTION (HOURS) 



Fig. 12. The synthesis of TMV ribonucleic acid in Nicotiana tabacum after infec- 

 tion with TMV (measured by local lesion test in Nicotiana glutinosa). [From R. 

 Engler and G. Schramm, Nature 183, 1227 (1959).] 



faster since all the RNA is packed into protein after 80-110 hours. There- 

 fore, the amount of free RNA reaches a maximum about 45 hours after 

 infection and decreases afterwards. 



By chromatographic studies on extracts from infected plant tissue using 

 cation and anion exchanging cellulose adsorbents, it was possible to identify 

 two infectious components with different chromatographic behavior. 135 

 One component was not adsorbed on the ion exchange column and lost its 

 infectivity after ribonuclease treatment. This is probably free RNA. The 

 other adsorbed to the column but could be eluated between pH 3.8 and 4.0 

 near the isoelectric point of TMV, and was not inactivated by ribonuclease. 

 Many typical TMV rods could be seen when this fraction was studied with 

 the electron microscope. Thus, this component is probably intact virus. 

 The relative amounts of the two components are dependent on the length 

 of infection. More RNA was found after shorter infection (9 days) and 

 significantly more virus in extracts of plants infected for 6 months. It is 

 well known that RNA is unstable in the usual tissue extract and, therefore, 

 it is questionable if the quantitative data are significant. Further, it is not 

 known whether the chromatographic treatment has any effect on the in- 

 fectivity of RNA. This should be tested since it is well known that in- 

 fectious RNA is sensitive towards certain salts and salt concentrations. 



135 G. W. Cochran and J. L. Chidester, Virology 4, 390 (1957). 



