PHOSPHATIDYLINOSITOL 4-KINASE - GENE STRUCTURE AND REQUIREMENT FOR YEAST-CELL VIABILITY

Phosphatidylinositol (PtdIns) 4-kinase catalyzes the first step in the biosynthesis of PtdIns-4,5-bisphosphate (PtdIns[4,5]P2). Hydrolysis o f PtdIns[4,5]P2 in response to extracellular stimuli is thought to ini tiate intracellular signaling cascades that modulate cell proliferatio n and differentiation. The PIK1 gene encoding a PtdIns 4-kinase from t he yeast Saccharomyces cerevisiae was isolated by polymerase chain rea ction (PCR) with oligonucleotides based on the sequence of peptides de rived from the purified enzyme. The sequence of the PIK1 gene product bears similarities to that of PtdIns 3-kinases from mammals (p110) and yeast (Vps34p). Expression of PIK1 from a multicopy plasmid elevated PtdIns 4-kinase activity and enhanced the response to mating pheromone . A pik1 null mutant was inviable, indicating that PtdIns4P and presum ably PtdIns[4,5]P2 are indispensable phospholipids.