Tor, a phosphatidylinositol kinase homologue, controls autophagy in yeast. Autophagy is a process of bulk protein degradation induced by starvation. The study shows that Tor negatively regulates autophagy. When rapamycin, an inhibitor of Tor function, is added, autophagy is induced even in nutrient-rich medium. A temperature-sensitive tor mutant also leads to autophagy induction at nonpermissive temperatures. Tor is the first molecule identified as a key player in the starvation-signaling pathway of autophagy. Additionally, high concentrations of cAMP inhibit autophagy. APG gene products are involved in autophagy induced by starvation. Autophagy is not induced in apg mutants in the presence of rapamycin, indicating that Tor acts upstream of Apg proteins. In nutrient-rich medium, Apg proteins are also involved in the transport of aminopeptidase I from the cytosol to the vacuole. Tor may switch Apg function between autophagy and transport of aminopeptidase I. Nutrient starvation induces autophagy in both yeast and mammalian cells. Autophagy is mediated by the process of delivering cytoplasmic components to lysosomes. The study shows that Tor is involved in the signaling pathway from nutrient starvation to G1 arrest in yeast. Rapamycin, an immunosuppressive drug, is effective in arresting yeast at early G1 phase. The effect of rapamycin is mediated by FKBP, and the FKBP-rapamycin complex binds to Tor. Inactivation of both Tors leads to G1 arrest. Tor2p has another essential function in the organization of the actin cytoskeleton. Tor1p does not have this function. To investigate the control mechanism of autophagy in yeast, the effects of inactivating Tor and high concentrations of cAMP were determined. The study found that Tor function is involved in the induction of autophagy in yeast. Inactivation of Tor by rapamycin treatment or using a temperature-sensitive allele of TOR2 promotes autophagy even under nutrient-rich conditions. The results suggest that Tor functions by blocking a factor needed for initiation of autophagy. This model is consistent with what is known in mammalian cells, where the condition for phosphorylation of the ribosomal protein S6 is inhibitory for autophagy. S6 phosphorylation is sensitive to rapamycin, suggesting that a rapamycin-sensitive factor is involved upstream of S6 phosphorylation and autophagy. The factor is assumed to be RAFT/FRAP, the mammalian counterpart of Tor, which mediates S6 kinase activity. The study also found that cAMP inhibits autophagy. The results indicate that increasing the concentration of cAMP inhibits autophagy even in the presence of rapamycin. The inhibitory effect of cAMP is observed in mammalian cells. The studyTor, a phosphatidylinositol kinase homologue, controls autophagy in yeast. Autophagy is a process of bulk protein degradation induced by starvation. The study shows that Tor negatively regulates autophagy. When rapamycin, an inhibitor of Tor function, is added, autophagy is induced even in nutrient-rich medium. A temperature-sensitive tor mutant also leads to autophagy induction at nonpermissive temperatures. Tor is the first molecule identified as a key player in the starvation-signaling pathway of autophagy. Additionally, high concentrations of cAMP inhibit autophagy. APG gene products are involved in autophagy induced by starvation. Autophagy is not induced in apg mutants in the presence of rapamycin, indicating that Tor acts upstream of Apg proteins. In nutrient-rich medium, Apg proteins are also involved in the transport of aminopeptidase I from the cytosol to the vacuole. Tor may switch Apg function between autophagy and transport of aminopeptidase I. Nutrient starvation induces autophagy in both yeast and mammalian cells. Autophagy is mediated by the process of delivering cytoplasmic components to lysosomes. The study shows that Tor is involved in the signaling pathway from nutrient starvation to G1 arrest in yeast. Rapamycin, an immunosuppressive drug, is effective in arresting yeast at early G1 phase. The effect of rapamycin is mediated by FKBP, and the FKBP-rapamycin complex binds to Tor. Inactivation of both Tors leads to G1 arrest. Tor2p has another essential function in the organization of the actin cytoskeleton. Tor1p does not have this function. To investigate the control mechanism of autophagy in yeast, the effects of inactivating Tor and high concentrations of cAMP were determined. The study found that Tor function is involved in the induction of autophagy in yeast. Inactivation of Tor by rapamycin treatment or using a temperature-sensitive allele of TOR2 promotes autophagy even under nutrient-rich conditions. The results suggest that Tor functions by blocking a factor needed for initiation of autophagy. This model is consistent with what is known in mammalian cells, where the condition for phosphorylation of the ribosomal protein S6 is inhibitory for autophagy. S6 phosphorylation is sensitive to rapamycin, suggesting that a rapamycin-sensitive factor is involved upstream of S6 phosphorylation and autophagy. The factor is assumed to be RAFT/FRAP, the mammalian counterpart of Tor, which mediates S6 kinase activity. The study also found that cAMP inhibits autophagy. The results indicate that increasing the concentration of cAMP inhibits autophagy even in the presence of rapamycin. The inhibitory effect of cAMP is observed in mammalian cells. The study