98 Discussion 



would say that this gene was responsible for a shift in the production of 

 one haemoglobin as against another, whereas in fact it is responsible for 

 suppressing one potentiality and the persistence of another one. This is 

 a difficulty which can be applied to any possible case of mutation 

 affecting the specific properties of protein which have been produced. 

 You have no way of telling whether the original genotype could have 

 produced this new protein if it had "wanted" to, perhaps changing the 

 conditions under which it may "want" to. If we disregard that, we can 

 allude to a considerable series of mutational changes of antigenic speci- 

 ficity in the protein of the flagella of Salmonella, which are rather readily 

 selected for by means of antiserum. Here we have unusually favourable 

 conditions for the detection of mutational changes affecting the specific 

 configuration of the protein, but a detailed analysis of the chemical 

 basis of the observed changes in immunological specificity remains to be 

 done. 



Pollock: That may be what the trouble is. Is it not possible that there 

 you have simply got a change in the position of the antigens ? 



Lederberg: Absolutely, but this consideration and the one I stated 

 before will apply to any experiment of this kind. Until we know how 

 two types of protein are being made, so that we can say that one is being 

 made as the direct causal alternative to the other, we shall always be 

 able to say that we are shifting the quantitative or even topographical 

 relations of the products of a cell. 



Pollock: You mean that even if an enzyme of type A is formed in a 

 particular strain, and on mutation a functionally similar enzyme, but 

 of type B, is formed; and that if then one were quite unable to detect 

 any trace of type A enzyme in the mutant, one could always say that 

 there were traces there but they were too feeble to be detected. 



Lederberg: This would apply to haemoglobin in adult man. 



Pollock: I agree, but I was visualizing the possibility of there being 

 a change in the structure of the system that was responsible for forming 

 the protein ; that one might substitute itself for the other and that they 

 could not really exist together. 



Lederberg: I am not proposing that any bacterium is potentially 

 capable of producing any enzyme that humans do. I am proposing that 

 this is rather a sterile question as far as experimental procedures at the 

 present time are concerned, until we understand more directly the way in 

 which specific proteins are formed and how they are determined by the 

 genetic material. 



Barber: Was it possible, by a simple process of enzyme adaptation, 

 to increase penicillinase production in strain 5 ? 



Pollock: No, the 5 and 5P and 5B strains are not inducible under any 

 conditions; nor do they give rise to inducible mutants. 



Alexander: Since in successive generations the amount of penicillinase 

 per bacterium goes down, have you proved that this is because the 

 amount produced by each individual organism goes down, or could it be 

 that they are just getting diluted out, i.e. that some retain the full 

 activity and some don't produce any? 



Pollock: It could be the latter, yes. It would be very interesting to 



