me 



d2i 

 di9 

 die 

 die 

 dt4 



di7 



ms ! igi 



d34 d,22 



d32 d30/ 



C COI 



his 



:co2; 



391 



P4 



mi 



C02 44-34' 67 



1'^ I I h- 



97 



50 42 >^ COI 



H \ H^=ttf 



^v^ 

 Cj 



J L 



C| 



C2 



im 



FIGURE 43-1. Diagrammatic representation of the linkage group of the temperate 

 bacteriophage X. The upper diagram shows the linear arrangement of various 

 markers for host range or plaque size or type. The d symbols refer to specific de- 

 fective mutants. The c region is marked by a thicker line and is shown enlarged in 

 the lower diagram. It is composed of three sub-regions, c., Ci, C2. Im refers to 

 the segment controlling immunity. {After F. Jacob and J. Monod.) 



completely lambda except for the Ci region of 

 the lambda genetic map. Such a hybrid 434 

 still behaves as 434 in the following respects. 

 It still occupies only the 434 position in the 

 E. coli map, and makes the cell immune only 

 to subsequent infection by 434 or hybrid 434. 

 We may conclude from this that the Ci region 

 of lambda is the only portion of the lambda 

 genotype concerned with selecting its par- 

 ticular prophage site on the chromosome, and 

 the only essential portion determining im- 

 munity to infection by homologous phage. 

 Let us restate these results in terms of lambda 

 prophage. Since the characteristics of pro- 

 phage include its association with a particular 

 chromosomal site and with the immunity of 

 its host, it is concluded that both these traits 

 of prophage are intimately associated only 



with the Ci portion of the phage genome. 

 We shall also call Ci the "prophage region" 

 of other phage genomes. 



Whereas different Ci mutants of lambda 

 can undergo recombination, there is no re- 

 combination between the Ci's of lambda and 

 434, indicating a genetic dissimilarity between 

 them. It becomes clear that the presence of 

 a given Ci region inhibits the vegetative multi- 

 plication of superinfecting particles possessing 

 the same Ci regions. This immunity is found 

 to be due to the occurrence of a repressor 

 substance, in the cytoplasm, whose formation 

 and specificity appear to be determined by 

 the Ci region. 1 



1 The preceding discussion is based primarily upon 

 work of F. Jacob and E. L. Wollman (1957), of 

 A. D. Kaiser and F. Jacob (1957), and of F. Jacob 

 and A. Campbell. 



FIGURE 43-2. Part of the E. coli linkage map showing the location of certain inducible prophages. 



Lac, Galb 82 X 434 



--I 1 \ 1 h- 



424 

 381 21 1466 



H 1 h+— • 



