264 ANNUAL REPORT SIMITHSONIAN ESrSTTTUTION, 1942 



acid type. Bushy stunt virus appears to contain about 83 percent 

 protein and 17 percent of a nucleic acid of the same kind as that 

 found in tobacco mosaic virus. Tobacco ring spot virus contains 40 

 percent nucleic acid, the highest percentage yet found in a virus. This 

 is also of the yeast nucleic acid type, but the elementary bodies of 

 vaccinia and of psittacosis have been found to give a test character- 

 istic of thymus nucleic acid. With the exception of a bacteriophage 

 preparation obtained by Kalmanson and Bronfenbrenner and con- 

 sidered to be a simple protein, all the purified virus preparations so 

 far obtained have been at least as complex as a nucleoprotein. This 

 fact may eventually prove of prime importance, for it may be re- 

 called that chromosomes appear to consist almost exclusively of 

 nucleoprotein. Some viruses appear to contain in addition some car- 

 bohydrate, others lipoid, and still others appear to be so complex 

 that they may be indistinguishable from bacteria in composition. The 

 distribution of amino acids in the protein component of tobacco mo- 

 saic virus has been studied, and at present only the apparent absence 

 of histidine and the lack of a preponderance of arginine and of 

 other known basic amino acids are noteworthy. The complete amino 

 acid distribution in strains of this virus and in other viruses has not 

 been determined as yet, although such studies are in progress and 

 may provide a clue to the reason for the specificity of viruses and 

 possibly a means for distinguishing not only between viruses but 

 also between the strains of a virus. For example, with Dr. EJiight 

 it has already been found that the amounts of certain aromatic 

 amino acids vary with the strain of the virus. Analysis of 12 prep- 

 arations of tobacco mosaic virus indicated the presence of 3.8, 4.5, and 

 6.0 percent of tyrosine, tryptophane, and phenylalanine, respectively, 

 with maximum deviations of ±0.1 percent for the tyrosine and ±0.2 

 percent for the tryptophane and phenylalanine values. The corre- 

 sponding values in the case of the Holmes ribgrass strain of tobacco 

 mosaic virus were 6.4, 3.5, and 4.3 percent and 3.8, 1.4, and 10.2 per- 

 cent in the case of the closely related cucumber mosaic virus 4. These 

 results are of considerable importance, since they show that the 

 mutation of tobacco mosaic virus with the formation of a new 

 strain which in turn causes a new disease may be accompanied by 

 changes in the amino acid composition of the virus. The fact that the 

 phosphorus content of the different strains was approximately the 

 same may be taken as an indication of the absence of significant 

 quantitative differences in the nucleic acid component of the strains. 

 Because of the close similarity between the properties of viruses and 

 those of the bearers of heredity, it is obvious that an extension of 

 this work should provide information of a fundamental nature 

 regarding the structural changes involved in the mutation within 

 chromosomes. The nature of the structural alterations which must 



