The Ras‐GTPase activating proteins Ira1p and Ira2p are required for proper control of phosphatidylinositol deacylation and glycerophosphoinositol transport in Saccharomyces cerevisiae.

Abstract

Phospholipase B‐mediated deacylation of phosphatidylinositol (PI) results in the formation of extracellular glycerophosphoinositol (GroPIns). GroPIns is transported across the Saccharomyces cerevisiae plasma membrane into the cell via the transporter encoded by GIT1. We screened the yeast viable knockout set for mutants unable to grow when GroPIns was added as sole phosphate source. Our selection criteria identified strains bearing deletion mutations in IRA1 and IRA2 as being defective for growth on GroPIns. Ira1p and Ira2p are known to act as Ras‐GTPase activating proteins. Not only do ira1Δ, ira2Δ and ira1Δira2Δ mutants display decreased GroPIns transport activity, but also an increase in extracellular GroPIns production, with the ira1Δira2Δ double mutant displaying the most extreme phenotypes. These results suggest that hyperactivation of the RAS/cAMP signaling pathway upregulates the production of extracellular GroPIns via phospholipase B‐mediated PI turnover and downregulates the transport of GroPIns into the cell via Git1p. This research was supported by NIH grant GM59817 to J.P.‐V.