GENETIC RECOMBINATIONS LEADING TO PRODUCTION OF 



ACTIVE BACTERIOPHAGE FROM ULTRAVIOLET 



INACTIVATED BACTERIOPHAGE PARTICLES 1 



S. E. LURIA and R. DULBECCO 



Department of Bacteriology, Indiana University, Bloominglon, Indiana 



Received June 28, 1948 



THE potentialities of bacteriophage genetics have been revealed by the 

 discovery of genetic recombinations among related phage particles in- 

 fecting the same bacterial cell (Delbruck and Bailey 1946). The complexities 

 of these genetic systems have been further illustrated by the work of Hershey 

 and Rotman (1948) on a number of different genetic determinants involved 

 in the determination of the alternative phenotypes r + and r in phage T2H. 

 A different approach to the genetic mechanisms of bacteriophages originated 

 from the chance observation by Delbruck and Bailey that, after exposure 

 to ultraviolet light, some phages gave variable plaque counts, depending on 

 the relative concentrations of phage lysates and host cells at the time of assay. 

 In investigating this phenomenon, one of us (Luria 1947) discovered a mecha- 

 nism of phage reactivation by interaction among inactive particles in the 

 course of intracellular growth. The detailed investigation of this phenomenon 

 has indicated new possibilities for a quantitative analysis of the genetic struc- 

 ture of these viruses and has suggested a possible mechanism for their repro- 

 duction. 



A preliminary discussion of some of the results reported in this paper has 

 appeared (Luria 1947) ; their implications for a number of problems have been 

 discussed in a forthcoming publication (Luria 1948). The present article is 

 intended to present the results in detail, and, by describing techniques and 

 methods of analysis, to serve as a background for future publications on this 

 topic. 



The analysis of the results presented in the following pages is based on the 

 hypothesis that inactivation of bacteriophage particles by ultraviolet light is 

 due to production of discrete alterations in individual portions of genetic ma- 

 terial. Although the internal evidence in support of this hypothesis, as pre- 

 sented in this paper, is quite satisfactory, it must be said that satisfactory 

 external evidence from other lines of attack is not yet available. The conclu- 

 sions reached in this article must be considered for the time being as working 

 hypotheses for further investigation. 



MATERIAL AND GENERAL METHODS 



The system of phages T1-T7, their r mutants, and their common host 

 Escherichia coli strain B have repeatedly been described, as well as the use of 



1 This work was done under an American Cancer Society grant recommended by the 

 Committee on Growth of the National Research Council. We wish to acknowledge the able 

 assistance of Mrs. J. P. Headdy. 



[Reprinted by permission from Genetics 34:93-122, March, 1949] 



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