202 



ERNST FREESE 



TABLE V 

 Rates of Reversion Induction for Base Analog Inducible Mutants 



From Freese (1961) 



q/^, rate of increase of the frequency of revertants per viable phage and per lethal hit, 

 in units 10"*, measured by directly plating phages on bacteria, E. coli B (all viable 

 phages give plaques) and on K (selective, rll mutants do not, but revertants do, grow). 

 a/^ is the same rate but the treated phages were preadsorbed to UV killed bacteria B 

 (survival 10"', and the infectd centers plated on K; .'\P, HA, and N mutants induced by 

 AP, HA, and Bl', respectively;— , not measured;^ , smaller than or about equal to. 



agents that produce transitions. For this conclusion it is unessential 

 that some of the little in(iucible mutants show induced suppressor muta- 

 tions, as for example, AP 70, which gives after EES induction only 

 revertants that form big standard type plaques on bacteria B. 



One would like to argue that the highly inducible mutants have a 

 G-C pair at their mutant site and that the above agents can induce their 

 back mutations. Here the problem of suppressor mutations does play an 

 important role in the interpretation. Functional tests (on K and B) of 

 induced revertants have shown that for mutants AP 72 and AP 275 

 (see Table V) most revertants have standard phenotype; for AP 41 

 both standard type revertants (on K and B) and others with tiny 

 plaques on K (and plaques on B) have been observed; for AP 114 less 



