Identification of a nuclear pheromone-sensitive protein kinase not identical to p34CDC28 in Saccharomyces cerevisiae

Nuclei of Saccharomyces cerevisiae cells contain a protein kinase, the activity of which is drastically reduced in response to an activation of the mating signal pathway by pheromone. Inhibition of this pheromone-sensitive kinase is also observed under conditions of constitutive activation of the signal pathway in a temperature-sensitive cdc70 mutant. The enzyme, which by SDS-PAGE has a molecular mass of 34,500 Da, is a protein serine kinase that phosphorylates several endogenous substrates in nuclear extracts. The activity of this kinase is temperature-resistant in a temperature-sensitive cdc28 mutant, indicating that it is not identical to p34CDC28, the catalytic component of the cell cycle protein kinase complex.