SBF CELL-CYCLE REGULATOR AS A TARGET OF THE YEAST PKC-MAP KINASE PATHWAY

Protein kinase C (PKC) signaling is highly conserved among eukaryotes and has been implicated in the regulation of cellular processes such a s cell proliferation and growth. In the budding yeast, PKC1 functions to activate the SLT2(MPK1) mitogen-activated protein (MAP) kinase casc ade, which is required for the maintenance of cell integrity during as ymmetric cell growth. Genetic studies, coimmunoprecipitation experimen ts, and analysis of protein phosphorylation in vivo and in vitro indic ate that the SBF transcription factor (composed of Swi4p and Swi6p), a n important regulator of gene expression at the G(1) to S phase cell c ycle transition, is a target of the Slt2p(Mpk1p) MAP kinase. These stu dies provide evidence for a direct role of the PKC1 pathway in the reg ulation of the yeast cell cycle and cell growth and indicate that cons erved signaling pathways can act to control key regulators of cell div ision.