The early biochemical consequences of inositol starvation in an inositol auxotroph of Saccharomyces cerevisiae were examined as a means of determining the cellular role of inositol. Upon withdrawal of inositol, the rate of incorporation of 32P-labeled inorganic phosphate into phosphatidylinositol and into the phosphoinositol-containing sphingolipids immediately dropped by 80 and 50%, respectively; however, synthesis of the other major phospholipids continued for 2 to 3 h at control rates. The

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... corporation of [U-4C]glucose into cell wall glycans began to decline immediately poststarvation and decreased to 50% of the initial rate by 80 min for mannan and by 140 min for alkali-and acid-insoluble glucan. These changes in the rates of synthesis of cell wall glycan and phosphatidylinositol were the earliest effects of inositol starvation, preceding inhibition of the synthesis of protein and ribonucleic acid as measured by incorporation of radioactive precursors into trichloroacetic acid-insoluble cell material. These results suggest that phosphatidylinositol may play a direct role in the synthesis or secretion of yeast glycans. 79 on May 8, 2020 by guest