Chapter II 

 The Biochemistry of Plant Viruses 



Roy Markham 



Agricultural Research Council, Virus Research Unit, 

 Cambridge, England 



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 



1. Turnip Yellow Mosaic Virus 40 



2. Gradient Centrifugation 41 



E. Following the Course of a Purification 42 



1. Infectivity Measurements 43 



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 Polypeptide Chains 48 



1 . Determination of Amiuo Acid Composition 48 



2. Determination of the Nature of the Chain Ends 49 



3. Determination of Sequence 49 



IV. The Nucleic Acids 51 



A. The General Structure of Nucleic Acids 53 



1 . Nucleosides 53 



2. Nucleotides 54 



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 7O 



A. Chemical Composition 7I 



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 



VOL. II— 3 33 



