Catalyzes the transfer of phosphatidylinositol (PI) between membranes (By similarity). Binds PI (PubMed:10400687). Also binds phosphatidylcholine (PC) and phosphatidic acid (PA) with the binding affinity order of PI > PA > PC (By similarity). Regulates RHOA activity, and plays a role in cytoskeleton remodeling (By similarity). Necessary for normal completion of cytokinesis (By similarity). Plays a role in maintaining normal diacylglycerol levels in the Golgi apparatus (By similarity). Necessary for maintaining the normal structure of the endoplasmic reticulum and the Golgi apparatus (By similarity). Required for protein export from the endoplasmic reticulum and the Golgi (By similarity). Binds calcium ions (By similarity). a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol)(in) = a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol)(out) Interacts with PTK2B via its C-terminus. Interacts with RHOA. Has higher affinity for the inactive, GDP-bound form of RHOA. The CDK1-phosphorylated form interacts with PLK1. Interacts with VAPB and PIK4CA (By similarity). Peripheral membrane protein associated with Golgi stacks in interphase cells. A minor proportion is associated with the endoplasmic reticulum. Associated with lipid droplets. Dissociates from the Golgi early on in mitosis and localizes to the cleavage furrow and midbody during cytokinesis. Detected at high levels in brain, and at lower levels in lung, kidney, spleen and liver (at protein level). Ubiquitous. Highly expressed in embryonic retina and the central nervous system. Detected at low levels during fetal development up to day 15. Highly expressed at day 17. Phosphorylated on multiple sites by CDK1 at the onset of mitosis. Phosphorylation facilitates dissociation from the Golgi complex and is required for interaction with PLK1 (By similarity). Phosphorylated on threonine residues upon treatment with oleic acid. Phosphorylated on tyrosine residues by PTK2B. Belongs to the PtdIns transfer protein family. PI transfer class IIA subfamily.