CHARACTERISTICS OF SPONTANEOUS REVERTANTS IN HAPLOID YEAST

The appearance dynamics of spontaneous revertants in adenine- or leuci ne-auxotrophic haploid Saccharomyces cerevisiae strains has been studi ed using mathematical simulation methods. In the case of adenine auxot rophs an increase in the number of revertants with decreasing metaboli te content is found to result mainly from increasing the rate of intra genic suppressor mutations. In the case of leucine auxotrophs revertan ts result from increasing the appearance of mutants formed at similar rates under different cultivation conditions. In the latter case the a ppearance of mutant colonies increases with decreasing size of colonie s of the initial auxotrophic cells. The last can simulate so-called ad aptive mutagenesis. The heterogeneity of revertants appearing in diffe rent time periods is described.