GENETICS 



LYSOGENY AND GENETIC RECOMBINATION 

 IN ESCHERICHIA CO LI K12 



by 



Elie L. Wollman and Frangois Jacob 



Presented by Jacques Trefouel 



Crosses between E. coli K12 Hfr and F^, both Ij'sogenic, show that the X pro- 

 phage and Gal 4 are situated on the segment TL LaCj. Spontaneous induction 

 of the prophage suppresses those of the zygotes which received a X prophage 

 whenever the Hfr parent is lysogenic and the F" parent non-lysogenic. This 

 modifies the distribution among the recombinants of characters Unked to the 

 X prophage. 



It had been supposed until now that the presence of the X prophage 

 does not alter the results of genetic analysis of E. coli K12. The phe- 

 nomenon of spontaneous induction observed in the course of crosses 

 between lysogenic Hfr (ly+) bacteria and non-lysogenic F~ (ly~) 

 bacteria established the fact that in the course of certain crosses an im- 

 portant fraction of the zygotes can be eliminated.' One might ask whether 

 this elimination does not affect preferentially some segments of genetic 

 material, thus exercising a counterselection with respect to certain classes 

 of recombinants. In particular, it might be possible to explain in this way 

 the anomalies found in crosses of the type F+ ly+ X F~ ly~.^ 



In crosses of Hfr T+ L+ S^ X F" T" L" S^ in which the bacteria are 

 mixed in the proportion of 1 Hfr bacterium for 20 F~ bacteria the fre- 

 quency of recombination (the number of T+ L+ S'' recombinants divided 

 by the initial number of Hfr) varies considerably according to the actual 

 cross carried out. This frequency, which is of the order of 5 to 10% for 

 crosses Hfr ly+ X F~ ly~, surpasses 50% in crosses of Hfr ly+ X F~ 

 ly+ and of Hfr ly- X F" ly". 



Translated from the French and reprinted by permission of the 



authors and the Imprim^rie Gauthier-Villars from the Comptes 



Rendus des Seances de l'Academie des Sciences, 239, 



455-456 (1954). 



334 



