biostudies-literatureWallace RLUniversity of ArizonaNational Institute of General Medical SciencesNIGMS NIH HHSe68773https://www.ebi.ac.uk/biostudies/studies/S-EPMC9499541biostudies-literatureUnknown11The target of rapamycin complex I (TORC1) regulates cell growth and metabolism in eukaryotes. Previous studies have shown that nitrogen and amino acid signals activate TORC1 via the highly conserved small GTPases, Gtr1/2 (RagA/C in humans), and the GTPase activating complex SEAC/GATOR. However, it remains unclear if, and how, other proteins/pathways regulate TORC1 in simple eukaryotes like yeast. Here, we report that the previously unstudied GPCR-like protein, Ait1, binds to TORC1-Gtr1/2 in <i>Saccharomyces cerevisiae</i> and holds TORC1 around the vacuole during log-phase growth. Then, during amino acid starvation, Ait1 inhibits TORC1 via Gtr1/2 using a loop that resembles the RagA/C-binding domain in the human protein SLC38A9. Importantly, Ait1 is only found in the <i>Saccharomycetaceae/eLifeAit1 regulates TORC1 signaling and localization in budding yeast.PMC9499541R01 GM097329R01GM097329T32GM136536T32 GM136536Wallace RLLu ELuo XCapaldi APfalseAit1 regulates TORC1 signaling and localization in budding yeast.The target of rapamycin complex I (TORC1) regulates cell growth and metabolism in eukaryotes. Previous studies have shown that nitrogen and amino acid signals activate TORC1 via the highly conserved small GTPases, Gtr1/2 (RagA/C in humans), and the GTPase activating complex SEAC/GATOR. However, it remains unclear if, and how, other proteins/pathways regulate TORC1 in simple eukaryotes like yeast. Here, we report that the previously unstudied GPCR-like protein, Ait1, binds to TORC1-Gtr1/2 in <i>Saccharomyces cerevisiae</i> and holds TORC1 around the vacuole during log-phase growth. Then, during amino acid starvation, Ait1 inhibits TORC1 via Gtr1/2 using a loop that resembles the RagA/C-binding domain in the human protein SLC38A9. Importantly, Ait1 is only found in the <i>Saccharomycetaceae/2022-01-01T00:00:00Z2022 Sep2025-04-26T22:06:51.606Z2025-04-06T17:04:25.135ZS-EPMC94995413604776210.7554/eLife.68773