The Physiology of Mutants Derepressed for Sporulation in Saccharomyces cerevisiae

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Abstract
The spd 1 mutants of S. cerevisiae are affected in the initiation of sporulation since they sporulate under conditions in which the wild-type does not. They are unable to grow on a range of non-fermentable C substrate, but can grow on ethanol. On others including acetate, glycerol, lactate and pyruvate, the mutants sporulate abundantly, even in rich media. The mutation does not affect the uptake of glycerol or the synthesis of the enzymes concerned with its entry into general metabolic pathways. It probably affects a central metabolic function concerned with the metabolism of some but not all non-fermentable C sources. The spd 1 mutation is also expressed in haploids. When haploid or diploid cells are transferred to media containing only non-fermentable C substrates they become arrested in the G1 phase of the cell cycle before or at the execution point for the cdc28 mutation. In diploids homozygous for the spd1 gene these conditions also lead to a lowering of the repression by the N source. The spd 1 mutants are therefore probably not affected directly in events unique to the initiation of sporulation, but in areas of metabolism closely connected with the arrest of cells in the G1 phase of the cell cycle and the control of induction of sporulation.