CHAPTER 

 VI 



VIRUS ACTION AND REPLICATION* 



James E. Darnell, Jr., M.D. 



INTRODUCTION 



VV HEN the genetic composition of organisms is tiiought of in 

 terms of information storage, it is immediately apparent why 

 viruses, which represent the smallest storehouses of biological 

 information, and thus probably the least complicated, have been 

 such popular research tools. Since the discox'cry of the nucleo- 

 proteinic and molecular nature of viruses in 1936, the study of 

 virus action and replication has contributed greatly to the present 

 knowledge of how genetic information is stored and expressed. 

 I will limit my discussion primarily to a summary of the events 

 in bacteriophage infection, the most thoroughly understood virus 

 cycle, and to a brief discussion about recent work using poliovirus 

 as a model for studying animal virus replication. 



MACROMOLECULAR EVENTS IN 

 BACTERIOPHAGE INFECTION 



Bacteriophage infection is initiated by attachment of the phage 

 particle to a susceptible cell followed by the injection of the DNA 

 of the phage through a hole produced in the cell wall by a lyso- 

 zyme contained within the phage tail (1). 



Two types of response to infection by phage may occur in 

 bacteria: 1) the lytic response in which phage multiplication is 

 accompanied by cell death and lysis; 2) the lysogenic response in 

 which the phage genome becomes integrated with the host cell 



*This work was supported in part by a research grant from the National Institutes 

 of Health (C-5789}. 



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