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      RAFT1: A mammalian protein that binds to FKBP12 in a rapamycin-dependent fashion and is homologous to yeast TORs

      , , , ,
      Cell
      Elsevier BV

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          Abstract

          The immunosuppressants rapamycin and FK506 bind to the same intracellular protein, the immunophilin FKBP12. The FKB12-FK506 complex interacts with and inhibits the Ca(2+)-activated protein phosphatase calcineurin. The target of the FKBP12-rapamycin complex has not yet been identified. We report that a protein complex containing 245 kDa and 35 kDa components, designated rapamycin and FKBP12 targets 1 and 2 (RAFT1 and RAFT2), interacts with FKBP12 in a rapamycin-dependent manner. Sequences (330 amino acids total) of tryptic peptides derived from the 245 kDa RAFT1 reveal striking homologies to the yeast TOR gene products, which were originally identified by mutations that confer rapamycin resistance in yeast. A RAFT1 cDNA was obtained and found to encode a 289 kDa protein (2549 amino acids) that is 43% and 39% identical to TOR2 and TOR1, respectively. We propose that RAFT1 is the direct target of FKBP12-rapamycin and a mammalian homolog of the TOR proteins.

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          Most cited references26

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          Single-step purification of polypeptides expressed in Escherichia coli as fusions with glutathione S-transferase

          Plasmid expression vectors have been constructed that direct the synthesis of foreign polypeptides in Escherichia coli as fusions with the C terminus of Sj26, a 26-kDa glutathione S-transferase (GST; EC 2.5.1.18) encoded by the parasitic helminth Schistosoma japonicum. In the majority of cases, fusion proteins are soluble in aqueous solutions and can be purified from crude bacterial lysates under non-denaturing conditions by affinity chromatography on immobilised glutathione. Using batch wash procedures several fusion proteins can be purified in parallel in under 2 h with yields of up to 15 micrograms protein/ml of culture. The vectors have been engineered so that the GST carrier can be cleaved from fusion proteins by digestion with site-specific proteases such as thrombin or blood coagulation factor Xa, following which, the carrier and any uncleaved fusion protein can be removed by absorption on glutathione-agarose. This system has been used successfully for the expression and purification of more than 30 different eukaryotic polypeptides.
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            Targets for cell cycle arrest by the immunosuppressant rapamycin in yeast

            FK506 and rapamycin are related immunosuppressive compounds that block helper T cell activation by interfering with signal transduction. In vitro, both drugs bind and inhibit the FK506-binding protein (FKBP) proline rotamase. Saccharomyces cerevisiae cells treated with rapamycin irreversibly arrested in the G1 phase of the cell cycle. An FKBP-rapamycin complex is concluded to be the toxic agent because (i) strains that lack FKBP proline rotamase, encoded by FPR1, were viable and fully resistant to rapamycin and (ii) FK506 antagonized rapamycin toxicity in vivo. Mutations that conferred rapamycin resistance altered conserved residues in FKBP that are critical for drug binding. Two genes other than FPR1, named TOR1 and TOR2, that participate in rapamycin toxicity were identified. Nonallelic noncomplementation between FPR1, TOR1, and TOR2 alleles suggests that the products of these genes may interact as subunits of a protein complex. Such a complex may mediate nuclear entry of signals required for progression through the cell cycle.
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              Fluorescence detection in automated DNA sequence analysis.

              We have developed a method for the partial automation of DNA sequence analysis. Fluorescence detection of the DNA fragments is accomplished by means of a fluorophore covalently attached to the oligonucleotide primer used in enzymatic DNA sequence analysis. A different coloured fluorophore is used for each of the reactions specific for the bases A, C, G and T. The reaction mixtures are combined and co-electrophoresed down a single polyacrylamide gel tube, the separated fluorescent bands of DNA are detected near the bottom of the tube, and the sequence information is acquired directly by computer.
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                Author and article information

                Journal
                Cell
                Cell
                Elsevier BV
                00928674
                July 1994
                July 1994
                : 78
                : 1
                : 35-43
                Article
                10.1016/0092-8674(94)90570-3
                7518356
                b8014cd0-dcb1-4221-b70b-b8df02262e1b
                © 1994

                https://www.elsevier.com/tdm/userlicense/1.0/


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