Catalyzes the biosynthesis of phosphatidylinositol (PtdIns) as well as PtdIns:inositol exchange reaction. May thus act to reduce an excessive cellular PtdIns content. The exchange activity is due to the reverse reaction of PtdIns synthase and is dependent on CMP, which is tightly bound to the enzyme. a CDP-1,2-diacyl-sn-glycerol + myo-inositol = a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol) + CMP + H(+) Divalent metal cations; Mn(2+) or Mg(2+). Inhibited by PtdIns (product inhibition), phosphatidylinositol phosphate, and nucleoside di- and tri-phosphates. Optimum pH is 9.0. Optimum temperature is 50 degrees Celsius. Detected in placenta (at protein level). Widely expressed. Higher expression in adult liver and skeletal muscle, slightly lower levels seen in pancreas, kidney, lung, placenta, brain, heart, leukocyte, colon, small intestine, ovary, testis, prostate, thymus and spleen. In fetus, expressed in kidney, liver, lung and brain. Belongs to the CDP-alcohol phosphatidyltransferase class-I family.