Genetic and biochemical characterization of the yeast spo12 protein

We have performed a genetic and biochemical analysis of the SPO12 gene, whi ch regulates meiotic nuclear divisions in budding yeast. When sporulated, s po12 mutants undergo a single meiotic nuclear division most closely resembl ing meiosis II. We observed that Spo12 protein is localized to the nucleus during both meiotic divisions and that Clb1-Cdc28, Clb3-Cdc28, Clb4-Cdc28, and Clb5-Cdc28 kinase activities during meiosis were not affected by a spo1 2 mutation. Using two-hybrid analysis, we identified several genes, three o f which are meiotically induced, that may code for proteins that interact w ith Spo12p. We also observed that two genes, BNS1 (Bypasses Need for Spo12p ), which has homology to SPO12, and SPO13, whose mutant phenotype is like t hat of spo12, can partially suppress the meiotic defect of spo12 mutants wh en overexpressed. We found that Spo12p is also localized to the nucleus in vegetative cells and that its level peaks during G2/M. We observed that a s po12 mutation is synthetically lethal in vegetative cells with a mutation i n HCT1, a gene necessary for cells to exit mitosis, suggesting that Spo12p may have a role in exit from mitosis.