passages.id: split_6_test_1611_passage
passages.type: progene_text
passages.text: Two distinct structural families of phosphoinositide ( PI ) kinases have so far been identified and named after their prototypic members , the PI 3-kinase and phosphatidylinositol ( PtdIns ) phosphate kinase families , both of which have been found to contain structural homologues possessing PI 4-kinase activity .