LYSOGENY 349 



There is one instance, however, in which the relationship that exists 

 between a virus and a higher organism parallels to an amazing extent the 

 situation which has been established in the case of lysogenic bacteria. This 

 is the classic case of CO 2 sensitivity in Drosophila, which has been extensively 

 studied by L'Heritier, and his group (I'Heritier, 1954). The factor responsible 

 for CO 2 sensitivity has all the properties of a virus, and can be transmitted by 

 injection from COg-sensitive flies to normal individuals. Inheritance of CO 2 

 sensitivity in Drosophila is one of the classic examples of maternal inheritance, 

 since stable CO 2 sensitivity is only transmitted in crosses in which the females 

 bear the character. In such "stabilized" individuals, the virus appears to be 

 integrated in a noninfectious form and is present in every single egg laid by 

 the female. Although stabilized lines are very reminiscent of lysogenic bacteria 

 in many of their properties, the inheritance of the character appears to be 

 better explained by a cytoplasmic rather than by a nuclear localization of 

 the provirus. 



Despite this difference, the factor responsible for CO 2 sensitivity in 

 Drosophila appears to have all the properties of a provirus. It therefore seems 

 probable that other known or yet unknown cases of latency of viruses of 

 animals or plants will also prove to be a reflection of the existence of a 

 provirus state. The recent developments made in the methods of growth of 

 animal viruses in pure cell cultures (Dulbecco and Vogt, 1953; Puck et al., 

 1956) show that, for this class of viruses at least, this possibility is not 

 remote. 



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