518 KAISER AND JACOB 



recipient lysogenic for X an average of 22 % (75 + 103/397 + 398) of the 

 gal+ transductants were nonlysogenic. But when the donor was lysogenic 

 for 434 and the recipient lysogenic for \, 9% (39 + 23/298 + 400) of 

 the gal+ were nonlysogenic. In the reciprocal transductions where the 

 donor was lysogenic for X and the recipient lysogenic for 434hy or for 

 434, the frequencies of nonlysogenic strains among the gal+ were 9% 

 (36/415) and 15% (18/120), respectively. The significance of the differ- 

 ences in each case is questionable for two reasons. First, differences of 

 the same order were observed when the same transduction was repeated 

 with independent isolates of the same donor strain, as may be seen by 

 comparing examples A and B in Table 4. Second, the hypothesis that 

 prophage 434hy and prophage 434 occupy different loci would require 

 that a particular order be assignable to the loci of the three prophages 

 involved. Neither the order X ~ 434 — 434hy nor the order X — 434hy — 

 434 is consistent with the frequencies of nonlysogenic transductants ob- 

 served in reciprocal transductions. For, whereas the order X — 434 — 

 434hy might have been indicated when the donor was lysogenic for 434 

 or for 434hy and the recipient lysogenic for X due to a greater frequency 

 of nonlysogenic strains in the latter transduction than in the former, 

 the reverse order X — 434hy — 434 would have been indicated by the 

 reciprocal transductions when the donor was lysogenic for X, due to a 

 greater frequency of nonlysogenic transductants when the recipient was 

 lysogenic for 434 than when the recipient was lysogenic for 434hy. 

 These data, therefore, are not incompatible with the idea that prophage 

 434hy occupies the same locus as prophage 434. 



Allelism of prophage 434hy to prophage 434 was independently con- 

 firmed by the bacterial cross Hfr T+L+S^ gal+(434) X F+T-L-S^(434hy) 

 gal~/X/434. Among 400 gal+S'' prototrophs no nonlysogenic strains were 

 found. 



Bacteria lysogenic for both X and 434 or for X and 434hy were found in 

 some of the transduction experiments reported in Table 4. Ten strains of 

 each type were examined in detail ; all of them had the following proper- 

 ties. They produced two types of phage, one type which plated on K12(X) 

 and another type which plated on K12(434). When induced with ultra- 

 violet light and plated, before lysis, on C600, they produced mottled 

 plaques like those of C600 mixedly infected with X and 434. These strains 

 were immune both to X and to 434 and did not support the growth of 

 T4r„. 



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