Phosphoinositide-specific phospholipase C interacts with phosphatidylinositol kinase homolog TOR2

The Saccharomyces cerevisiae PLC1 gene encodes a homolog of the delta isoform of mammalian phosphoinositide-specific phospholipase C. Cells deleted for PLC1 gene (plc1Delta) are viable but display several phenotypes, including temperature and osmotic sensitivity and defects in utilization of carbon sources other than glucose. We have used the two hybrid screen to identify Plc1p-interacting proteins. One of the identified proteins was Tor2p, a putative phosphatidylinositol (PtdIns) kinase involved in regulation of protein synthesis, cell cycle progression and organization of the actin cytoskeleton. This interaction was confirmed biochemically by coprecipitation of Plc1p and Tor2p. The results suggest that Tor2p, as a PtdIns kinase, produces phosphorylated PtdIns, which is then hydrolyzed by the associated Plc1p. The proximity of Tor2p to Plc1p may therefore result in a regulated spatial and temporal coupling of synthesis and hydrolysis of phosphorylated forms of PtdIns.