Recombination between Related Temperate Bacterio- 

 phages and the Genetic Control of Immunity and 

 Prophage Localization' 



A. D. Kaiser and F. Jacob 



Department of Microbiology, Washington University School of Medicine, St. Louis, 

 Missouri, and Service de Physiologic Microbienne, Institut Pastexir, Paris, France 



Accepted August 31, 1957 



Lysogenic bacteria are immune to infection with phage homologous to the 

 prophage. By means of crosses between phages showing different immunity 

 specificities it is shown that immunity specificity is determined by the same 

 segment of the phage genetic material that controls the ability of the phage 

 to lysogenize. Furthermore, this same segment, called the "ci region", also 

 determines which locus is occupied by the prophage on the chromosome of 

 Escherichia coli K12. 



INTRODUCTION 



Lysogenic bacteria possess and transmit to their offspring the power to 

 produce bacteriophage. The phage that lysogenic bacteria produce is 

 capable of making new lysogenic strains by infection of sensitive bacteria. 

 By morphological, serological, and genetic criteria, the phage produced 

 by such a lysogenized strain is identical with the phage used for the 

 lysogenizing infection. Thus each lysogenic bacterium carries all the 

 genetic information present in an infective phage particle. Nevertheless, 

 disruption of lysogenic bacteria fails to reveal infective particles. The 

 structure bearing the genetic information of the phage in a lysogenic 

 bacterium is called a "prophage" (Lwoff, 1953). There is strong evidence 

 that the prophage is the genetic material of the phage bound to a specific 

 site of the bacterial chromosome (Lederberg and Lederberg, 1953; 

 Wollman, 1953; Appleyard, 1953; Jacob, 1955). 



The presence of the prophage confers upon the host bacterium a re- 

 sistance to infection with the homologous phage and its mutants. This 



' Part of this work was supported by grant E-1275 from the National Insti- 

 tutes of Allergy and Infectious Diseases, National Institutes of Health, 

 Bethesda, Maryland. 



Reprinted by permission of the authors and Academic Press, Inc. 

 from Virology, 4 (3), 509-521 (1957). 



353 



