270 



supposition that the specific infectivity 

 of any TMV particles that might re- 

 main as contaminants in the protein 

 and RNA preparations is the same as 

 that possessed by the untreated control 

 TMV. 



Counts and length distributions were 

 secured for the particles of both TMV 



FRAENKEL-CONRAT AND WILLIAMS 



and the most active reconstituted virus, 

 the 25,000-rpm. pellet described above, 

 in order to ascertain the relative bio- 

 logical efficiency of the two materials 

 in terms of numbers of particles per 

 milliliter per lesions per leaf. The re- 

 sults of the counts and length distribu- 

 tions are given in Table 3. From this 



Table 3 



Electron Microscope Counts of Particles of TMV and Reconstituted Virus 

 AT Assay Concentration 



Assay Con- 

 centration Lesions/ 

 Preparation (M.g./Ml.) Half-Leaf 



Control TMV 0.1 10 



Reconstituted virus 



(25,000 rpm.) 10 10 



Total Particles/Ml. of 



Particles/All. Length 290-3 10 M^ 

 1.6 X 109 7.0 X 108 



2.2 X 1011 



2.0 X 1010 



Particles/Ml./ 

 10 Lesions 



7 X 108 



2 X 1010 



table it appears that about one-tenth 

 of the total particles in the reconsti- 

 tuted virus, representing about one- 

 third of the total mass, were of length 

 ca. 300 m|.i, the length of the monomer 

 of normal TMV. These particles were 

 therefore only about 3 per cent as in- 

 fective as the particles of similar length 

 in the control TMV. It thus appears 

 that polymerization of the protein by 

 nucleic acid to form ~300-m|i. rods is 

 fairly frequent but that only a fraction 

 of the rods is reconstituted with the 

 structural faithfulness necessary for 

 infectivity. 



The length distribution of the rods 

 of this pelleted material exhibited a 

 reasonably random character for 

 lengths less than about 260 m^i, but a 

 highly uniform length between 290 

 and 310 m|i^ for the 10 per cent of the 

 rods falling in this range. Only 3 per 

 cent of the particles were of lengths 

 greater than 310 m|i. This is in contrast 

 to aggregates of X-protein, which 

 show a complete randomness of dis- 

 tribution of lengths. 



To ascertain whether the nucleic 

 acid was localized in the center of the 

 newly formed virus rods. Dr. R. Hart 

 applied his technique of detergent 



Fig. 4. Particles of reconstituted TMV 

 treated briefly with hot detergent. Rods 

 are seen with strands of nucleic acid pro- 

 jecting from their ends. This appearance 

 is identical with that found for normal 

 TMV more severely treated. X55,000. 



