VIRUS-INDUCED ACQUISITION OF METABOLIC FUNCTION 35 



It may be suggested that the pursuit of these problems requires an 

 infectable cell transformable at high efficiency and a tiny phage pos- 

 sessing a bare minimum of DNA necessary for the inheritable trans- 

 mission of virulence. Is the bare minimum of DNA that in (j) x 174, and 

 how many proteins does the DNA complement of this phage control? 

 If only a single polypeptide chain is controlled in infections by (Jl x 174, 

 we may cease to worry about the requirement for transformability. 

 However, if this DNA determines the biosynthesis of several different 

 polypeptides, we shall wish to fractionate the DNA and introduce the 

 determinants separately ( as in bacterial transformation ) . We are at the 

 stage, therefore, at which the study of the molecular relations of DNA 

 as a genetic determinant and the protein produced as the expression 

 of this determinant will be markedly facilitated by finding new and 

 more simple biological systems to replace our old friend, T2. 



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