CHAPTER 28 



The Biological Role of the Pentose Nucleic Acids 

 J. BRACKET 



Page 

 I. The Role of PNA in Plant Viruses 476 



1. The Composition of Plant Viruses 476 



2. The Importance of PNA in Plant Virus Multiplication 476 



a. Abnormal Proteins from Virus-Infected Plants 476 



b. Interference with Virus Multiplication by Chemical Analogues of 

 Pyrimidines and Purines 477 



3. Mechanism of Virus Multiplication 478 



II. The role of PNA in Morphogenesis 478 



1. Morphogenetic Gradients and PNA Distribution 479 



2. Experimental Modifications of PNA Synthesis or Distribution: Effects 



on Morphogenesis 480 



a. Chemical Analogues of Purines and Pyrimidines 480 



b. Other Toxic Substances 481 



c. Physical Agents 481 



d. Abnormal Nuclear Composition 482 



3. Pentosenucleoproteins and Neural Induction 483 



III. PNA and Protein Synthesis 486 



1. Cytochemical and Biochemical Evidence for a Link between PNA and 

 Protein Synthesis 486 



a. Cytochemical Evidence 486 



b. Quantitative Evidence 488 



c. Additional Evidence 491 



2. Cellular Mechanisms of Protein Synthesis 493 



a. Short Summary of Caspersson's Theory 493 



b. New Facts since Caspersson's Theory . 495 



(1) Presence of PNA in Different Cytoplasmic Particles 495 



(2) Interrelations between Nuclear PNA and Cytoplasmic PNA . . 497 



(3) The Role of the Nucleus in Protein Synthesis 501 



(4) The Role of the Microsomes in Protein Synthesis 504 



3. Biochemical Mechanisms of Protein Synthesis 506 



a. Protein Synthesis by Reversal of Proteolysis 507 



b. Energy-rich Bonds in PNA Synthesis 509 



c. The ''Template" Hypothesis 510 



IV. Addendum 513 



The biological importance of pentosenucleic acids (PNA) is based on 

 three main lines of evidence: (1) the fact that all plant viruses so far studied 

 are composed of pentosenucleoproteins and that PNA is necessary for their 



475 



