Phosphatidylinositol-4-phosphate-5-kinase (PIPK) synthesizes phosphatidylinositol-4,5-bisphosphate, which regulates various processes including cell proliferation, survival, membrane trafficking and cytoskeletal organization. The PIPK family is divided into type I, type II and type III. Each type of the PIPK family phosphorylates distinct substrates. They contain an activation loop, which determines their enzymatic specificity and subcellular targeting. The phosphatidylinositol-4-phosphate-5-kinase type I consists of three members, PIPK I (alpha), (beta) and (gamma), which are characterized by phosphorylating PI4P on the 5-hydroxyl. PIPK I (alpha), designated PIPK I (beta) in mouse, is expressed in brain tissue. PIPK I (beta), designated PIPK I (alpha) in mouse, is also called STM7. PIPK I (gamma) has two variants produced by alternative splicing which are expressed in lung, brain and kidneys.