MITOSIS AND DNA CONTENT IN YEAST-CELLS OF ITERSONILIA-PERPLEXANS DERX

Four stages were distinguished in the mitotic cycle of the yeast phase of Itersonilia perplexans. Non-budding yeast cells showed both C1 and C2 levels of nuclear DNA corresponding to the G1 and G2 phases of the cell cycle, respectively. Budding yeast cells, either with a small or with a large bud, and with the nucleus still present in the mother cell, had only C2 levels of nDNA), corresponding to the G2 phase of the cell cycle. Divided nuclei had C1 levels of nDNA, corresponding to the G1 phase of the cell cycle. Our results indicate a delay of bud initiation until the G2 phase of the cell cycle. Hydroxyurea was found to suppress DNA synthesis to a large extent. nDNA content of the different yeast strains, based on nuclei in the G2 phase of the cell cycle, showed considerable differences. Four groups of strains with similar nDNA content were recognizable, which are in the proportion of 1.0 to 1.2 to 1.4 to 1.6. The variation in nDNA content may have resulted from duplication of chromosomes, followed by subsequent disappearance of part of the homologous chromosomes. Our results suggest the presence of aneuploidy among yeast strains of Itersonilia, which may be an important factor contributing to the variability of Itersonilia strains.