Endopolyphosphatases (Ppn1) from yeast and animal cells hydrolyze inorganic polyphosphate (poly P) chains of many hundreds of phosphate residues into shorter lengths (4, 1). The limit digest consists predominantly of chains of 60 (P₆₀) and 3 (P₃) P_i residues (4, 1). Ppn1p of Saccharomyces cerevisiae, a homodimer of 35-kDa subunits (about 352-aa) is of vacuolar origin and requires the protease activation of a 75-kDa (674-aa) precursor polypeptide (4, 1, 5). Null mutants in ppn1 accumulate long-chain poly P and are defective in growth in minimal media (1). A double mutant of PPN1 and PPX1 (the gene encoding a potent exopolyphosphatase) loses viability rapidly in stationary phase (1). Whether this loss is a result of the excess of long-chain poly P or to the lack of shorter chains (i.e., poly P₆₀ and P₃) is unknown (1). Overexpression of the processed form of Ppn1p should provide a unique and powerful reagent to analyze poly P when the chain termini are unavailable to the actions of polyPase and poly P kinase.

Last updated: 2002-01-14