The transcriptional regulator, Arg82, is a hybrid kinase with both monophosphoinositol and diphosphoinositol polyphosphate synthase activity

The Arg82 gene of Saccharomyces cerevisiae encodes a transcriptional regula tor that phosphorylates inositol 1,4,5-trisphosphate [Saiardi et al, (1999) Curr, Biol, 9, 1323-1326]. However, some controversy has surrounded the na ture of the reaction products. We now show that Arg82 phosphorylates inosit ol 1,3,4,5-tetrakisphosphate to inositol pentakisphosphate, which is itself converted to two isomers of diphosphoinositol tetrakisphosphate, one of wh ich has never previously been identified. One of the diphosphoinositol phos phates was further phosphorylated by a yeast cell lysate, We propose that A rg82 is an ancestral precursor of two distinct and specific enzyme families : inositol 1,4,5-trisphosphate kinases and diphosphoinositol polyphosphate synthases, (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B,V, ALL rights reserved.