VOL. 10 (1953) NUCLEIC ACID TRANSFER 



439 



TABLE VII 



TRANSFER OF ^2? FROM X-RAY INACTIVATED T4r 



Bacteria were mixedly infected with unlabelled T4r+ and X-ray irradiated 32p.iabelled T4r. 

 The adsorption of ^zp to bacteria was similar in the mixtures containing irradiated phage and in 

 control mixtures containing non-irradiated phage, being approximately 93 % in both cases. 



% of parental ^^P in 



Tube contents 



Low speed Progeny High speed 

 pellet phage supernatant 



Unlabelled T4r+ 



+ labelled T4r (non-irradiated) 11 43 46 



Unlabelled T4r+ 



+ labelled T4r (e-^ survival) 31 24 45 



Unlabelled T4r+ 



+ labelled T4r (e-* survival) 45 22 33 



Unlabelled T4r+ 



+ labelled T4r (e-i" survival) 42 30 28 



To answer this question we first carried out experiments with labelled phage 

 heavily irradiated with X-rays. Such particles retain the ability to adsorb to bacteria 

 while the majority of them have lost not only their infectivity, but also the ability to 

 kill the host cell and to transfer genetic specificity (WatsonI^). The experiments pre- 

 sented in Table VII show, however, that heavy X-ray damage reduces the transfer 

 values only from the normal 40 to 50% to about 25%. Thus, substantial amounts of 

 phosphorus may be transferred from particles which do not participate in genetic ex- 

 change. It should be noted that nearly 50% of the phosphorus of the irradiated particles 

 remain attached to the bacterial debris. This value is significantly greater than the 

 values of 5 to 15% found when active phage reproduces. It is possible that as many 

 as 50 % of the irradiation damaged phages remains passively attached to the cell surfaces ; 

 if so, the transfer value per transferring particle is again about 50%. 



Transfer of parental isotope without simultaneous genetic transfer can also be 

 demonstrated in bacteria in which one of the infecting phages does not multiply because 

 of the presence of an unrelated phage. This "mutual exclusion" (DelbruckI") is well 

 illustrated by the unrelated phages T3 and T4; if a bacterium is infected simultaneously 

 by both phages, T3 multipHcation is completely suppressed and only T4 progeny 

 particles appear; even the infecting T3 particles are lost. In Table VIII are shown the 

 results of an experiment in which bacteria were simultaneously infected with ^^P-Iabelled 

 T3 particles and unlabelled T4 particles. After lysis, the progeny particles were isolated 

 and tested for radioactivity, the specificity of which was shown by the extent of its 

 precipitation with anti-T3 and anti-T4 serum. It can be seen that approximately 25 % 

 of the 32p originally present in the T3 particles was transferred to the T4 progeny, 

 another 25% was associated with bacterial debris, while the remaining 50% cannot be 

 sedimented at high speed. The excluded phage thus does not sit passively on the bacterial 

 surface but must penetrate to the interior of the cell where it is broken down into its 

 simpler components. Our experiment, therefore, supports the conclusion of Weigle 

 AND Delbruck^^ that mutual exclusion must involve some mechanism other than the 

 establishment of a barrier to penetration. 

 References p. 442. 



112 



