CHEMISTRY AND VIRAL GROWTH 



whetlier the determinant of this character is the organ of at- 

 tachment itself or a different organ, that is, whether the gene 

 and the agent of its expression are the same or different sub- 

 stances. The following circumstances show that they are 

 difTerent. 



A single bacterium infected with both T2 and T4 yields a 

 mixed viral progeny among which the individual particles can be 

 classified in two ways. First, one can determine whether their 

 attachment to bacteria shows the specificity of T2 or the spec- 

 ificity of T4. This test shows that some particles resemble T2 

 and some T4. Second, one can classify the particles in terms of 

 the progenies they yield when they multiply individually. By 

 this test, too, some prove to resemble T2 and some T4. The 

 remarkable thing about the two tests is that they do not agree: 

 many particles adsorb like T2 and yield progenies like T4. The 

 best interpretation of this result is that, owing to the special 

 conditions prevailing in the mixedly infected bacterium, some of 

 the particles receive tail protein manufactured for a T2 particle, 

 together with a tail-protein-determining gene derived from the 

 T4 lineage, and vice versa. If so the two are different struc- 

 tures. The genetic results just described show that tail speci- 

 ficity, as such, is not conserved during reproduction. Analogous 

 radiochemical results show that tail substance is not conserved 

 during reproduction. Evidently tail protein is not the seed from 

 which new tail protein comes. These two results seem to 

 show that the injected materials direct the complete resynthesis 

 of tail protein. 



I have cited one item of a considerable body of genetic in- 

 formation (24) leading to the conclusion that the genetic mate- 

 rial of T2 consists of linear structures. All the chemical evidence 

 implicates DNA as the chief constituent of these structures. If 

 one wishes to assume that DNA is the prime hereditary material, 

 justification can be borrowed from the beautiful work of the past 

 decade with bacterial transforming systems (31), or it can be 

 sought directly, as will be discussed below. 



7 ..;/--•: .- 







