GTPase involved in activation of the TORC1 signaling pathway, which promotes growth and represses autophagy in nutrient-rich conditions (PubMed:26510498, PubMed:32801125). Also required for TORC1 inactivation during nitrogen starvation (By similarity). Required for intracellular sorting of GAP1 out of the endosome (PubMed:16732272). Functionally associated with the inorganic phosphate transporter PHO84, and may be involved in regulating its function or localization (PubMed:1620108). Heterodimer; with GTR2 (PubMed:21816923). Component of the GSE complex composed of GTR1, GTR2, SLM4, MEH1 and LTV1 (PubMed:16732272). Interacts with GTR2; the interaction is direct (PubMed:21816923). Interacts with TOR1 (PubMed:29698392). Decreases and delays activation of TORC1 signaling in nitrogen-replete conditions (glutamine nitrogen source) (PubMed:29698392). Abnormal punctate localization of PIB2 and TOR1 in nitrogen-replete conditions (glutamine nitrogen source) (PubMed:29698392, PubMed:32801125). Increases cellular levels of glutamine and alanine during high hydrostatic pressure (mechanical stress) (PubMed:32801125). Sensitive to high hydrostatic pressure (PubMed:32801125). Resistance to tunicamycin (endoplasmic reticulum stressor) administered together with FK506 (calcineurin inhibitor) (PubMed:26510498). Normal localization of KOG1 and TOR1 to the vacuolar membrane (PubMed:28483912). Simultaneous disruption of PIB2 results in TOR1 mislocalization and loss of TORC1 activity and viability (PubMed:29698392). Present with 907 molecules/cell in log phase SD medium. Belongs to the GTR/RAG GTP-binding protein family.