THE YEAST MCK1 GENE ENCODES A PROTEIN-KINASE HOMOLOG THAT ACTIVATES EARLY MEIOTIC GENE-EXPRESSION

We have identified a yeast gene, MCK1, that encodes a positive regulator of meiosis and spore formation. Sequence analysis revealed that MCK1 encodes a protein kinase homolog identical to YPK1, a phosphotyrosyl protein with demonstrated protein kinase activity. Increased MCK1 gene dosage accelerates the sporulation program; mck1 mutations cause delayed and decreased levels of sporulation. MCK1 is required during sporulation for maximal transcript accumulation from IME1, which encodes a meiotic activator. MCK1 is required in vegetative cells for basal IME1 expression, as evidenced by functional assays of an ime1-HIS3 fusion gene. MCK1 is also required for efficient ascus maturation. Although expression of IME1 from the GAL1 promoter restored high-level sporulation to mck1 mutants, it did not correct the ascus-maturation defect. This observation indicates that MCK1 is required, independently, for both the activation of IME1 and subsequent ascus maturation. Expression of an mck1-lacZ fusion gene was not regulated by the signals that govern meiosis. This observation is consistent with evidence that MCK1 plays a role in governing centromere function during vegetative growth as well as sporulation.