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+) (PubMed:3032971). According to PubMed:7998949 the cofactor is Mn(2+), while Mg(2+) is much less effective. Detected in liver (at protein level). Widely expressed. Highly expressed in the brain and kidney; lower levels in heart, spleen, lung, liver, skeletal muscle and testis. Inhibited by PtdIns (product inhibition). Belongs to the CDP-alcohol phosphatidyltransferase class-I family.