Cloning and Characterization of a GIT1 Homolog Gene from Schizosaccharomyces Pombe

Phosphatidylinositol (PI) deacylation in Saccharomyces cerevisiae results in the formation and excretion of glycerophosphoinositol (GPI). This is a predominant route of PI turnover and is not unique to S. cerevisiae. Released GPI can be transported back into the cell through a membrane permease encoded by the GIT1 gene, Git1p. Maximum transport is achieved in low inositol/low phosphate conditions at pHs below 7, and the addition of a protonophore to the GPI transport assay abolishes transport activity. These findings suggest that Git1p is a proton symporter. An excess of unlabeled glycerol-3-phosphate (G3P) inhibits the transport of radiolabeled GPI into S. cerevisiae. Furthermore, radiolabeled G3P is transported into S. cerevisiae in a Git1p-dependent fashion. A GIT1 homolog from Schizosaccharomyces pombe (Sp-git1) was cloned. Overexpression of Sp-git1 did not result in increased transport of GPI into S. cerevisiae or S. pombe cells. However, it resulted in increased transport of inositol in S. pombe