National Research Centre, Microbial Genetics Research Unit, Dokki, Cairo, U.A.R. (Egypt)
Results favour the view of Gutz (1961) “in cellular organisms the mutagenic action of nitrous acid may in part be an indirect one, affecting the DNA through changes in metabolism rather than by a direct deamination of its amino-bases”. In vitro, nitrous acid deaminates the purine and pyrimidine bases of RNA and DNA.
Transferring to complete media after incubation in Leupold's media (LM) lacking inositol helped in obtaining mutants. This method was more efficient in giving specific mutants than using LM supplemented with the specific requirements. However, it was possible by changing the concentration of NaNO2 and the time of incubation with LM media lacking inositol before transferring to obtain different kinds of mutants and different percentages of specific mutants, for instance, lysine- or arginine-requiring mutants.
Using the same methods for obtaining mutants with additional requirements with two arginine-requiring mutants and an adenine-requiring mutant was unsuccessful. The possible basis of this result had been discussed.
