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J Biol Chem. 1995 Sep 8;270(36):20875-8.

The rapamycin and FKBP12 target (RAFT) displays phosphatidylinositol 4-kinase activity.

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Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.


The immunosuppressant rapamycin prevents cell cycle progression in several mammalian cell lines and the yeast Saccharomyces cerevisiae. In mammalian cells, rapamycin binds to the small FK506-binding protein, FKBP12, allowing the drug-receptor complex to interact with the 289-kDa RAFT1/FRAP proteins. These proteins, along with their yeast homologs, TOR1/DRR1 and TOR2/DRR2, contain a C-terminal domain with amino acid homology to several phosphatidylinositol (PI) 4- and 3-kinases. However, no direct demonstration of kinase activity for this family of proteins has been reported. We now show that RAFT1, immunoprecipitated from rat brain and MG63 and HEK293 cells, contains PI 4-kinase activity and that rapamycin-FKBP12 has no effect on this activity. Thus, it is likely that, in vivo, rapamycin does not directly inhibit the PI 4-kinase activity and affects the RAFT1/FRAP protein through another mechanism.

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