In the nucleus, inositol hexakisphosphate kinase 1 (IP6K1) and 2 (IP6K2) phosphorylate inositol 5-diphospho-1,2,3,4,6-pentakisphosphate (5-PP-IP5) to inositol 5-triphospho- 1,2,3,4,6-pentakisphosphate (5-PPP-IP5) (Saiardi et al. 2001, Draskovic et al. 2008) and IP6K2 (Saiardi et al. 2001, Draskovic et al. 2008). While this reaction has been demonstrated to occur in vitro, the extent to which it occurs in vivo is less clear.