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 pheromo ne-sensitive kinase is also observed under conditions of constitutive activation of the signal pathway in a temperature-sensitive cdc70 muta nt. The enzyme, which by SDS-PAGE has a molecular mass of 34500 Da, is a protein serine kinase that phosphorylates several endogenous substr ates in nuclear extracts. The activity of this kinase is temperature-r esistant in a temperature-sensitive cdc28 mutant, indicating that it i s not identical to p34CDC28, the catalytic component of the cell cycle protein kinase complex.