Involved in negative regulation of the TOR signaling pathway in response to type of available nitrogen source. Inhibitor of PP2A phosphatase SIT4, which results in inhibition of nuclear export of MSN2, due to lack of dephosphorylation by SIT4. Also required for rapamycin induced activation of expression of many nitrogen discrimination pathway (NDP) genes. In complex with PPH21, required for organization of the actin cytoskeletom during the cell cycle via a Rho GTPase-dependent mechanism. Associates with the PP2a (PPH21 and PPH22) and SIT4 protein phosphatase catalytic subunits. Interacts with PPG1, PPH3 and TIP41. Phosphorylated by TOR kinases. Dephosphorylated by CDC55, TPD3 and SIT4. Belongs to the IGBP1/TAP42 family.