BIOCHEMICAL CHANGES IN YEAST DURING SPORULATION. II. ACETATE METABOLISM

Acetate metabolism was studied with Saccharomyces cerevisiae diploid strain G2-2 in sporulating culture, asporogenic diploid strains 3c × a and 3c × 3a, and respiratory deficient haploid strain 3c (asporogenic). Acetate in a sporulating medium was utilized by sporogenic and asporogenic diploid yeasts linearly with time. Activities of aconitase, NADP-linked isocitrate dehydrogenase, and succinate dehydrogenase initially increased in the cell-free homogenate of either strain. Activity of glucose-6-phosphate dehydrogenase decreased. Isocitrate lyase activity increased remarkably in the sporogenic strain but not in the asporogenic strain. The rate of production of ¹⁴CO₂ from ¹⁴C-1-acetate was accelerated more than from ¹⁴C-2-acetate in intact cells of the sporogenic strain during sporulating culture. Fractionation of radioactive cell substances showed remarkable lipid synthesis. Accumulation and reutilization of cold acid-soluble precursor substances occurred during sporogenesis. The role of glyoxylate and tricarboxylate cycle enzymes in sporulation is discussed.     

BIOCHEMICAL CHANGES IN YEAST DURING SPORULATION. I. FATE OF NUCLEIC ACIDS AND RELATED COMPOUNDS

Changes in nuclear figures and in activities of nucleic acid and protein syntheses were observed mainly on Saccharomyces cerevisiae G2-2 during sporogenesis. Patterns of DNA synthesis and of meiosis show that the sporogenic process in yeast was divided into an induction phase (I-phase), a DNA-synthesizing phase (S-phase) and a maturation phase (M-phase). Meiotic figures appeared most frequently at the end of the S-phase at approximately 12 hr in sporulation culture. In M-phase visible spores formed. The amount of protein increased in the initial 7 hr culture of 1-phase, then decreased in the S- and M-phases. But in sporulation culture of the asporogenic diploid strain 3c × a, protein did not decrease. RNA increased within 3 hr of the I-phase then stopped increasing. DNA synthesis occurred critically during S-phase, i.e. between 7 and 12 hr. and was somewhat resumed during the later part of M-phase. Oligodeoxyri-bonucleotide content decreased in the I- and M-phases and increased temporarily. Deoxyribosides decreased linearly during the sporogenic processes. Based on these results and results of experiments estimating the incorporation of ¹⁴C-uracil into nucleic acid and ¹⁴C-amino acid mixture into protein fractions, the roles of nucleic acid synthesis activities in meiosis and in sporulation are discussed.