Expression of the Saccharomyces cerevisiae PIS gene and synthesis of phosphatidylinositol in Escherichia coli.

Expression of the Saccharomyces cerevisiae PIS gene encoding phosphatidylinositol synthase in Escherichia coli was achieved by inserting its coding sequence into lacZ on pUC8. The fused gene encoded a phosphatidylinositol synthase whose amino-terminal three amino acids had been replaced by the amino-terminal five amino acids of E. coli beta-galactosidase. E. coli cells bearing this recombinant plasmid produced a significant level of phosphatidylinositol synthase in the presence of a lacZ inducer, isopropylthio-beta-D-galactopyranoside. When the culture medium was supplemented with myo-inositol and isopropylthio-beta-D-galactopyranoside, the cells accumulated a substantial amount of phosphatidylinositol in their membranes. When a saturating level of myo-inositol was added, phosphatidylinositol constituted about 4% of the total phospholipids. Phosphatidylinositol accumulation occurred at the expense of phosphatidylglycerol. The ratio of phosphatidylethanolamine to total acidic phospholipids remained constant. The growth rate of phosphatidylinositol-containing E. coli cells did not differ significantly from that of cells with the normal phospholipid composition.