GROWTH OF A MUTANT DEFECTIVE IN A PUTATIVE PHOSPHOINOSITIDE-SPECIFIC PHOSPHOLIPASE-C OF SCHIZOSACCHAROMYCES-POMBE IS RESTORED BY LOW CONCENTRATIONS OF PHOSPHATE AND INOSITOL

A mutant (plc1-1) of Schizosachar omyces pombe unable to grow on a min imal medium containing high amounts of phosphate was selected. On yeas t-extract agar its growth is temperature sensitive. Tests in liquid sy nthetic medium show that growth of the mutant is partially restored by lowering the phosphate and inositol concentrations in the growth medi um. The growth defect is fully suppressed by a plasmid encoding a puta tive protein having the structural features of phosphoinositide-specif ic phospholipases C (PI-PLC). This protein, of 899 amino-acids, contai ns the characteristic X and Y domains found in all PI-PLCs of higher a nd lower eucaryotes and reveals, in addition, an EF-hand motif (putati ve Ca2+-binding site). Like the corresponding enzyme from Saccharomyce s cerevisiae, the S. pombe PI-PLC is most similar-to the delta form of PI-PLC isoenzymes. The cloned gene integrates at the plc1 site indica ting that plc1 codes for a putative PI-PLC. Plc1 physically maps on th e left arm of chromosome II between rad11 and mei3.