MUTAGENESIS 117 



Lederberg: Doesn't the manganoiis do that? You know that from 

 experience. 



Za?nenhof: Yes. It has an entirely different redox potential. Ferrous 

 iron autooxydizes in the air but manganous does not. 



Novick: Manganese is a free radical agent. 



Lederberg: In reacting with oxygen? 



Novick: No. All kinds of free radicals. 



Lederberg: Of course, it does pick up an unpaired electron or it 

 could donate an electron to form a pair of radicals. I suppose one 

 question would be the relative effectiveness in aerobic and anaerobic 

 conditions. 



Demerec: Anaerobic is lower in effect than aerobic. 



Lederberg : Is it a very pronounced difference? 



Demerec: Quite pronounced, yes. 



Novick: What about the correlation of different kinds of mutations? 

 Have you tried more than one? 



Demerec: No. Only one kind of mutation was studied in detail, 

 namely, reversions from streptomycin dependence to nondependence. 

 At the time this work was done we assumed that we were observing 

 back mutations, but later work by Hashimoto (34) revealed that these 

 reversions are due to forward mutations in a suppressor locus, which 

 is closely linked to the region controlling streptomycin resistance. 

 However, we have evidence that MnCl2 is a potent mutagen for the 

 genes controlling resistance to phage Tl, lactose fermentation and five 

 steps in the synthesis of essential nutrients. I wish to add that Roberts 

 and Aldous (61) studied manganese metabolism, using our strain of 

 E. coli, and concluded that the manganese is adsorbed on proteins or 

 nucleic acid of the cell in a loosely bound complex, and that the 

 quantity adsorbed is determined mainly by the concentration of man- 

 ganese and other competing ions, and by the number of available 

 adsorption sites. 



Auerbach: In Penicillium, Sermonti (64) used manganese chloride, 

 and it had a very unexpected effect. Not only did it not produce muta- 

 tions or crossovers, but it suppressed the mutations which had been 

 induced by nitrogen mustard. I think that it acts in a very indirect 

 way. 



Demerec: You have asked me to say a few words about our current 

 work on mutations induced by 2-aminopurine and several other agents. 

 This work is being done with strain LT2 of Salmonella typhimurium. 

 We have a collection of about 4000 mutants, each of which originated 

 independently by forward mutation from the wild type. We find, as 

 has been reported in phages, two classes — those that have the capacity 



