Vm CONTENTS 



II. The Biochemistry of Plant Viruses by Roy Markham 33 



I. Introduction 35 



II. The Purification of Plant Viruses 36 



A. Growing the Virus- Infected Plants 37 



B. The Handling of the Virus-Containing Sap 38 



C. Clarification 39 



D. Centrifuge Separation Techniques 40 



E. Following the Course of a Purification 42 



III. The Protein Components of Plant Viruses 44 



A. Polypeptides 44 



B. The Determination of the Composition of Proteins 45 



C. Methods for the Determination of the Structure of Poly- 

 peptide Chains 48 



IV. The Nucleic Acids 51 



A. The General Structure of Nucleic Acids 53 



B. The Ribonucleic Acids 54 



C. The Finer Structure of the Ribonucleic Acids 55 



D. Deoxyribonucleic Acids 60 



E. Physical Properties of the Nucleic Acids 60 



V. The Tobacco Mosaic Virus 62 



A. Introduction 62 



B. The Virus in the Plant 64 



C. Purified Preparations 65 



D. Optical Properties 68 



VI. Properties of the Virus Protein 70 



A. Chemical Composition 71 



B. Evidence Relative to the Existence of Substructure 71 



C. The Amino Acid Composition of the Protein of a Typical 

 Tobacco Mosaic Virus 73 



D. The Polypeptide Subunit 74 



E. The Chain Ends 77 



F. The Position of the Nucleic Acid 79 



G. The A-Protein 80 



H. The X-Protein 81 



I. Effect of Heat on the Virus 82 



J. Reconstruction and the Infectivity of Virus Nucleic Acid 83 

 K. The Action of Various Agents upon the Infectivity of the 



Virus 85 



L. The Nucleic Acid of the Tobacco Mosaic Virus 86 



M. The Quantity of the Nucleic Acid in the Virus 88 



N. The Effect of the Host on the Virus 89 



0. Strains of the Tobacco Mosaic Virus 91 



VII. The Tomato Bushy Stunt Virus 93 



A. Purification 93 



