CHARACTERISTICS OF SPONTANEOUS MUTAGENESI S IN HAPLOID YEASTS

The dynamics of appearance of spontaneous revertants was studied in ha ploid strains of Saccharomyces cerevisiae, auxotrophic for adenine or leucine. Mathematic models of this process were used. It was confirmed that in the case of adenine auxotrophs, an increase in the number of revertants, depending on decreasing adenine content, was caused by a c hange in mutation rate of the ade2 gene. For leucine auxotrophs, a sim ilar phenomenon was determined by an increase in the rate of appearanc e of Leu(+) revertants due to a decrease in size of initial auxotrophi c cell colonies. Alteration in leucine content in the medium from 3 to 300 mg/l did not lead to a change in the reversion rate for the leu2 gene. The heterogeneity of revertants detected at different times was described.