IMMUNITY AND PROPHAGE LOCALIZATION 511 



TABLE 1 



Immunity and Host Range of Phages X, 434, 82, and 21 



Key: + indicates ability of phage to grow on the host; — indicates inability 

 to grow. 



Note: Loopfuls containing 2 X 10* or more phage particles were inoculated 

 onto the surface of an agar plate seeded with bacteria. Lysis of the bacteria within 

 the inoculated area was taken as the sign of phage multiplication. 



related to the gali~ of Morse et al. (1956), since it can be transduced to 

 gal+ by XHFT gala" but not by XHFT galr. 



Phages. Coli phages 434, 82, and 21 (Jacob and Wollman, 1956) are 

 capable of lysogenizing E. coli K 12. All three are serologically related to 

 phage X. Phage X is the wild type described previously (Kaiser, 1957). 

 The ability of phages X, 434, 82, and 21 to grow on various lysogenic and 

 resistant strains of E. coli K12 is shown in Table 1. It may be seen that 

 each phage is distinguished from the others by its ability to grow on all 

 of the lysogenic strains except the homologous one: each of the four 

 phages has a different immunity specificity. 



Crosses. The technique of crossing these phages is the same as the one 

 already described for XXX crosses (Kaiser, 1957). 



Because many stocks of X mutants are available, crosses were made 

 between X and each of the other phages. 



RESULTS 



1. Genetic recombination between X, 4^4, 82, and 21. The first series of 

 crosses involved phages 434, 82, or 21 as one parent, and X marked either 

 with ms, C02, Ci, coi, or mi as the other parent. A map giving the position 

 of the markers on the X linkage group is given in Fig. 1. The purpose of 

 these crosses is to see if 434, 82, and 21 carry and are able to transfer 

 to X the wild type alleles m5+, co^^, Ci+, coi+, and wt+. Thus, for example, 

 Xms, which forms medium-sized plaques, was crossed to 434 and the 

 offspring of the cross plated on K12(434), to examine only the phages 

 with the immunity specificity of X. The presence of some large plaques, 



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