Fig. 1.

Biosynthesis and signaling mechanisms of PP-InsPs. (A) Abbreviated biosynthetic pathway for PP-InsPs, involving the action of IP6K and PPIP5K in mammals (green). The corresponding enzymes in S. cerevisiae are shown in black. The pyrophosphate moiety can be cleaved by the mammalian phosphohydrolase hDIPP and the yeast proteins Ddp1 and Siw14. (B) PP-InsPs transmit information via two proposed mechanisms, protein binding and protein pyrophosphorylation, a covalent posttranslational modification. Specific examples for either mechanism are listed. hs, Homo sapiens; sc, S. cerevisiae.