TOR MUTATIONS CONFER RAPAMYCIN RESISTANCE BY PREVENTING INTERACTION WITH FKBP12-RAPAMYCIN

The antifungal, immunosuppressive compound rapa mycin arrests the cell cycle in G(1) in both yeast cells and T-lymphocytes. Previous genetic studies in yeast identified mutations in three genes, FPR1 (FKBP12), TOR1, and TOR2, which confer rapamycin resistance, and genetic findings implicated the TOR proteins as direct targets of FKBP12-rapamycin. Consistent with this model, we find that modulating TORI and TOR2 expression alters rapamycin sensitivity. We describe several TOR2 mutations that confer rapamycin resistance, These mutations prevent FKBP12-rapamycin binding to TOR2, as assayed with the two-hybrid system, We find that TOR1 and the mammalian TOR homologue (mTOR) also bind FKBP12 rapamycin, and mutations corresponding to those in TOR2 similarly block FKBP12-rapamycin binding, We demonstrate that FKBP12 prolyl isomerase activity is not required for FKBP12-rapamycin binding to TOR and that a composite protein drug surface contacts the TOR proteins, These studies confirm that the TOR proteins are direct targets of FKBP12-rapamycin, reveal that drug-resistant mutations prevent this association, and define structural features of these complexes.