VOL. 10 (1953) NUCLEIC ACID TRANSFER 435 



two low speed pellets were resuspended in broth and all fractions assayed for ^^p and 

 phage. Table I shows that 42.1% of the ^^p which initially adsorbed to the bacteria 

 and about 95% of the progeny phage was recovered in the high speed pellet. 



The radioactivity of the high speed pellet was characterized as belonging to phage 

 particles by precipitation with an excess of anti-T4 serum and by adsorption to sensitive 

 bacteria. Native as well as B/i adsorbed serum was used and in both cases 93% of 

 the ^2p was precipitated with the phage. Adsorption tests showed that over 90% of 

 the radioactivity adsorbed on B/i cells while less than 5% adsorbed on the resistant 

 strain B/3, 4, 7 on which T4 does not itself adsorb. These tests show that 90-95% of 

 the radioactivity in the high speed pellet is somehow associated with the phage particles. 



Before asserting that this ^^P is truly incorporated into the progeny phages, the 

 following possibihties must be considered: (i) degraded parental nucleic acids might 

 stay attached to the surface of the progeny particles, or (2) non-infective parental 

 particles might be adsorbed to the bacteria initially, released during lysis, and later 

 sediment together with the progeny particles. 



Both these possibihties are ruled out by the fact that the progeny particles from 

 an experiment like the one just described transfer their ^^P in exactly the same way 

 as did their uniformly labelled parents (Maaloe and Watson*). We, therefore, conclude 

 that about 95% of the ^^P in the high speed pellet is incorporated into the progeny 

 particles. Using this estimate in correcting for the phage present in the low speed pellets 

 and in the high speed supernatant, the fraction of the parental ^^p which has become 

 incorporated into the progeny particles is 45% in this experiment. 



Table II shows a series of similar experiments involving different stocks of labelled 

 T4r; it is notable that the differences in transfer are ve'"y small, usually less than 5%. 

 These values are not changed by varying the number of infective particles from i to 

 10 (the highest number tested). The amount of ^^P remaining attached to bacterial 

 debris is uniformly about 5 to 10%. If the different phage stocks had contained greatly 

 varying fractions of adsorbing but non-infecting phages, this would have caused the 

 low speed pellet values to fluctuate greatly. 



TABLE II 



EXPERIMENTAL VARIATION IN ^'P TRANSFER VALUES FOR T4r 



^^P transfer from secondarily adsorbed phage 



The experiments given in Table III show that particles which adsorb on a bacterium 

 more than two minutes after a primary infection with T4r transfer insignificant amounts 

 of ^^P. This was demonstrated by infecting bacteria with an average of 5 non-labelled 

 phages per cell and at various times later reinfecting with labelled phage. Column i 

 References p. 442. 



108 



