Macromolecular changes and commitment to sporulation in the fission yeast Schizosaccharomyces pombe1

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Abstract
Homothallic cultures of Schizosaccharomyces pombe in stationary phase may be induced to flocculate by aeration. Flocculation is followed by copulation, conjugation, zygote formation, meiosis and sporulation. This developmental sequence was monitored for respiratory activity, changes in protein, RNA and DNA, catabolite repression, and commitment to sporulation. Respiratory activity, apparently a prerequisite to induction, increased 5-fold prior to maximum flocculation and remained at that level up to the end of the sequence. Protein and RNA content increased prior to conjugation but gradually decreased shortly thereafter. A round of premeiotic DNA synthesis occurred after copulation, presumably during conjugation. The developmental sequence was repressible by glucose. Cyclic AMP at low concentrations stimulated sporulation somewhat, but the stimulatory effect was not sufficient to offset repression due to glucose. Commitment to sporulation was determined by adding glucose at various times during the developmental sequence and then observing refractoriness of the events to catabolite repression. Cells not committed were repressed by glucose and reverted to mitotic cell cycles. Committed cells proceeded to sporulate in the presence of exogenous glucose. Commitment to sporulation appears to occur soon after premeiotic DNA synthesis.