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ber of enzyme precursors or functional precursors. You made the statement 

 that when it does go in under certain circumstances, it can only go in by bump- 

 ing something out. 



SPIEGELMAN: Well yes, it can stay in only by bumping something out. 

 However, this replacement process is probably part of the mechanism of getting 

 the material fixed properly in the chromosomes. The picture that most of us 

 have at the present time of these so-called transduction phenomena is somewhat 

 as follows: Imagine a chromosome of the host recipient cell and a small seg- 

 ment carried in by the transducing virus agent. We know that homologus chrom- 

 osomes tend to synapse. It is not therefore, unreasonable to suppose that the 

 small piece carried in by the viral agent will pair off with the corresponding 

 portion of the homologus chromosome. If you now have a double cross-over, 

 then the only thing that can happen is that the piece which had been in goes out 

 and the new piece is inserted in its place in the chromosome. I think it is true 

 that most of us are disturbed by one consequence of this type of explanation. It 

 requires a very high frequency of double cross-overs in very small regions. 

 However, at the present moment it explains all the facts thus far available. 



KAMEN: Do you see any loss of any property as a consequence of in- 

 corporation of this foreign material? 



SPIEGELMAN: You can get both losses and gains depending upon where 

 you take your genetic area. 



KAMEN: That is what I mean. How are these losses absorbed? You 

 gained a galactose positive trait, but what did you lose'' 



SPIEGELMAN: You lose the galactose negative locus -- well, to give 

 you another case, streptomycin resistance can be lost and you can convert by 

 such transduction phenomena into streptomycin-sensitive. This has also been 

 accomplished by transformation. 



BENNETT: Is it at the same place presumably? 



SPIEGELMAN: There is no cell yet, and the big search is on now in a 

 lot of laboratories to get a cell in which you can do transformation,^ transduction 

 and classical recombination and then find out what the relation is between the 

 three. 



BENNETT: You mean as far as absolute site is concerned? 



SPIEGELMAN: That is right. Recently in our department, Lennox 

 has demonstrated transduction in coli K-12 which is able to recombine. So we 

 have two of those now. If we can get a transformation for E. Coli , then we will 

 have all three in one organism, and this is really what is needed to study the 

 relationship. 



KAMEN: Isn't Salmonella a good candidate for this purpose? 



SPIEGELMAN: Salmonella can be transduced but not transformed. 



POTTER: From the standpoint of nucleic acid metabolism after irradi- 

 ation, can you speculate on why the transduction is always of one character? 

 Are there any exceptions to this? 



SPIEGELMAN: Yes. Stocker has a case which is very strong for 



