558 S. E. LURIA 



the removal of external cell constituents that might interfere with attack on 

 new host cells. 



E. Phage Maturation and Infective Heredity 



The interpretation of phage maturation as the terminal assembly of 

 a specific core of viral DNA with specific proteins synthesized by the 

 virus-infected cell under viral control leads to several predictions as to 

 possible events that may take place at maturation or affect the occurrence of 

 maturation. 



1. Transduction 



In the course of vegetative replication and maturation, a phage particle 

 may occasionally come to include in its protein shell some fragment of the 

 bacterial genome. This gives rise to "transduction," as observed in Salmo- 

 nella (Zinder, 1953), in the coli-dysentery group (Lennox, 1955), and prob- 

 ably also in the genus Bacillus (Brown et al., 1955). In this tyjje of trans- 

 duction, the phage can transfer from one cell to another any group of closely 

 linked host genes. If the ceU survives infection, it may show one or more of 

 the transduced characters. 



In at least one other instance, with phage A, the only host genes that can 

 be transferred are some that were chromosomal neighbors of the prophage in 

 a lysogenic ceU, including a group of factors controlling utilization of galac- 

 tose (Morse et al., 1956). Here the transducing particles appear to have incor- 

 porated the fragment of host genome in the place of a portion of the phage 

 genome itself (Arber et al., 1957). This transducing phage thereby becomes 

 incomplete and ineffective in initiating its own reproduction, although it can 

 stiU produce cell lysis. This "defective" phage has become a specific trans- 

 ducer of the galactose determinants, which behave here as infective genetic 

 factors. There is now evidence (Luria et al., 1958) that other instances of 

 transduction may also reflect associations of bacterial genes with defective 

 phage. 



2. Defective Prophages 



If maturation is the culmination of a process of specific phage-controlled 

 biosynthesis, we may expect that both environmental agents and genetic 

 changes will affect the very occurrence of maturation. An example of an 

 environmental efTect is the specific prevention of successful phage assembly 

 and maturation by inhibitors such as the acridine dye, proflavine (DeMars, 

 1956). The defective prophages, on the other hand, provide examples of 

 genetic effects on maturation (Appleyard, 1954; Jacob and Wollman, 1956a). 



