A sample of food was found to induce mutation in E. coli in high frequency. The

Question

A sample of food was found to induce mutation in E. coli in high frequency. The single active ingredient was found to be the chemical saltpeter. Several arg- mutants were obtained after treatment with the compound. The abilities of known mutagens to reverse the saltpeter mutations (to arg+) were determined with a large number of the induced mutants. The frequency of arg+ cells among total cells after treatment was:
control: 6.8*10^-6
saltpeter: 5.8*10^-6
5-bromouracil: 6.1*10^-4
2-aminopurine: 8.0*10^-4
acridine: 7.0*10^-6
hydroxylamine: 6.9*10^-6
What DNA base changes are caused by the food laced with saltpeter? Explain reasoning

Explanation / Answer

Transitions are mutations in which one pyrimidine (C or T) is substituted by the other and one purine (G or A) is substituted on the complementary strand. In this case GC To AT saltpeter appears to work like hydroxylamine which cannot bring about reversion of a GC to AT transition.

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