Restoration of inositol prototrophy in the fission yeast Schizosaccharomyces pombe

The biosynthesis of inositol requires only two enzymes, inositol-l-phosphat e synthase (encoded by INO1) and an inositol monophosphatase, but the regul ation of inositol biosynthesis is under multiple controls and is exquisitel y regulated. In the budding yeast Saccharomyces cerevisiae, mutations in an y of 26 different genes lead to inositol auxotrophy. The fission yeast Schi zosaccharomyces pombe, however, is a natural inositol auxotroph. An investi gation has been initiated to examine the possible reasons that might have l ed to inositol auxotrophy in Sch. pombe. Complementation with a genomic lib rary of an inositol prototrophic yeast indicated that a Pichia pastoris INO 1 gene alone could confer inositol prototrophy to Sch. pombe and that the g ene was absent in Sch. pombe. To investigate possible reasons for the loss of INO1 gene in Sch. pombe, an attempt was made to disrupt inositol homeost asis in Sch. pombe by overproduction of intracellular inositol, but this di d not lead to any discernible adverse effects. The sources of inositol in t he natural environment of Sch. pombe were also examined. As the natural env ironment of Sch. pombe contains significant amounts of phytic acid (inosito l hexaphosphate), an investigation was carried out and it was discovered th at Sch. pombe can utilize phytic acid as a source of inositol under very sp ecific conditions.