The study identifies Rag GTPases as novel activators of the Target of Rapamycin complex 1 (TORC1) in response to amino acid signals. In Drosophila S2 cells, knockdown of Rag gene expression suppressed the stimulatory effect of amino acids on TORC1. In mammalian cells, expression of constitutively active Rag enhanced TORC1 activity in the absence of amino acids, while dominant negative Rag blocked the stimulatory effects of amino acids. Genetic studies in Drosophila also show that Rag GTPases regulate cell growth, autophagy, and animal viability under starvation conditions. These findings establish a novel function for Rag GTPases in TORC1 activation in response to amino acid signals.The study identifies Rag GTPases as novel activators of the Target of Rapamycin complex 1 (TORC1) in response to amino acid signals. In Drosophila S2 cells, knockdown of Rag gene expression suppressed the stimulatory effect of amino acids on TORC1. In mammalian cells, expression of constitutively active Rag enhanced TORC1 activity in the absence of amino acids, while dominant negative Rag blocked the stimulatory effects of amino acids. Genetic studies in Drosophila also show that Rag GTPases regulate cell growth, autophagy, and animal viability under starvation conditions. These findings establish a novel function for Rag GTPases in TORC1 activation in response to amino acid signals.