Chapter VI 



The Chemical Basis of the Infectivity of Tobacco Mosaic Virus 

 and Other Plant Viruses 



H. Fraenkel-Conrat 

 Virus Laboratory, University of California, Berkeley, California 



I. Purification of Plant Viruses 430 



A. Procedure for the Preparation of TMV 430 



B. Isolation and Properties of Other Plant Viruses 430 



C. The Nature of Virus-Specific Components in Infected Plants 432 



II. Degradation of TMV 433 



A. Preparation of Nucleic Acid 433 



B. Preparation of Protein 435 



C. Structure and Function of Viral Proteins 435 



III. Assay of Infectivity of TMV and TMV-RNA 437 



IV. Reconstitution of TMV 439 



V. Infectivity of Viral RNA 441 



A. TMV 441 



B. Other Viruses 445 



C. Natural Occurrence of Infectious Nucleic Acid 446 



VI. Chemical and Physicochemical Properties of Infectious TMV-RNA 446 



A. Molecular Weight 446 



B. Lability 448 



C. Miscellaneous Reactions 450 



VII. Reconstitution of Viruses from Different Strains 450 



A. IMixed Viruses 451 



B. Mixed Nucleic Acid Viruses 452 



C. Search for in Fi'^ro-Produced Mutants 453 



References 455 



A survey of the properties of those viruses which have been chemically 

 characterized shows that the plant viruses consist only of nucleic acid and 

 protein, while animal viruses range from this simplest composition to con- 

 siderably more complex compositions. In regard to the nature of the nucleic 

 acid, all known plant viruses contaLa only ribonucleic acid (RNA), while 

 either deoxyribonucleic acid (DNA) or RNA may occur in animal and 

 bacterial viruses. It appears possible that RNA viruses have a separate 

 evolutionary history, possibly older than that of the DNA-containing viruses . 

 On the other hand, the great resemblance in composition, both quaUtative 

 and quantitative, between many plant and animal viruses of both types 

 suggests a close functional resemblance for the different groups of viruses. 

 The occurrence of a seemingly constant amount of RNA in all viruses con- 

 taining this nucleic acid, notwithstanding the great variations in their sizes, 



429 



