1 30 Information Storage and Neural Control 



(55, 56). Under the usual experimental conditions Rous infected 

 cells do not lyse but become transformed after one to three days 

 into tumor cells which grow as changed clones of cells. Each 

 transformed cell is capable of liberating" virus at a very slow rate 

 while continuing to grow. This kind of integration between virus 

 and cell has no counterpart in bacteriophage systems. 



In none of the animal virus systems studied is there any detailed 

 knowledge of how the damaging effect of the invading virus is 

 mediated, nor is there any understanding of how the tumor 

 viruses become integrated with the cell. 



ANIMAL VIRUSES: FORMATION OF VIRAL 

 PRECURSOR MOLECULES 



It will be recalled from the phage work that two classes of 

 macromolecules are formed after phage infection: 1) messenger- 

 RNA and "early" enzyme proteins in which the ultimate function 

 is to allow phage replication, and 2) the phage precursor DNA 

 and proteins which eventually form the new particles. In the case 

 of animal viruses this first class of new products has not been 

 proved definitely to exist. There are several reported instances 

 of materials which are apparently formed by infected cells after 

 virus infection, but whether these are genetically specified by the 

 infecting virus is unknown. This group of materials includes 

 interferon, which is produced by a variety of cells after infection 

 by a variety of viruses (57), a cell detachment factor produced 

 by adenovirus infected HeLa cells, which is serologically distinct 

 from the virus (58) and arginase, which is increased in cells 

 infected with papilloma virus (59). There is no apparent con- 

 nection between the formation of any of these substances and the 

 replication of the virus concerned. 



Studies on newly formed products in infected cells have, there- 

 fore, been limited largely to the study of virus precursor molecules. 

 The techniques that have been most useful in identifying the time 

 and place of both synthesis of viral precursor molecules and 

 maturation of whole virus particles are: electron microscopy, 

 flourescent antibody staining and other types of immunologic 

 identification, extraction and measurement of infectious nucleic 

 acid, and radioisotopic labeling and purification of virus. 



