RADIOBIOLOGY OF BACTERIOPHAGE 



369 



tested for multiplicity reactivation in K12(A); (2) a mixture of an rllA 

 mutant stock and an rllB mutant stock was irradiated and tested for multi- 

 plicity reactivation in the same fashion. The only difference between the 

 two experiments is that in Experiment (2) a smaller number of wild-type 

 rll cistrons is introduced into each cell. It was found that at all doses tested 

 (up to 9 hits per phage), the survival of the wild-type multicomplexes was 

 higher than the survival of the mixed rll multicomplexes. 



4 8 12 16 

 Phage -lethal UV-hits, r 



Fig. 8. Multiplicity reactivation of ultraviolet-irradiated T4 in Escherichia coli 

 K12(A). A mixture of equal numbers of rllA and rllB particles was irradiated and 

 adsorbed at low (0.24 particles per cell) multiplicity on K12(A). The smooth curve is 

 the sum of the theoretical survival curves for bi- and tricomplexes weighed according to 

 their relative fiequency among productive cells at zero dose. On the assumption that 

 rll cistrons act as vulnerable centers in K12( A), the survivals of the bi- and tricomplexes, 

 respectively, are given by 



1/2 == [1 — (1 — e-/'-/«)2]'» e-o-i^r 

 2/3 = [1 — (1 — e->'''/«)3]« e-''-°"'"[l — (1 — e-o-o76r)2] 

 From Harm (1956) (see Fig. 4), we estimate /(the fraction of hits on vulnerable centers) 

 to be 0.4 and n to be 3. The number 0.15 is the fraction of hits on the rll cistrons (see 

 Fig. 7). The calculation of y^ was simplified by assuming that the two cistrons were of 

 equal sensitivity. For a total multiplicity of 0.24, the productive complexes at zero 

 dose have frequencies of 0.86 and 0.14, respectively, for the bi- and tricomplexes. The 

 data are from impublished experiments of Dr. R. H. Epstein. 



One experiment was performed under conditions which makes it possible 

 to test quantitatively (although not very critically) the notion that the rll 

 cistrons act as an additional pair of vulnerable centers when multiplicity 



VOL. II — 24 



