Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.5.1.18 (glutathione S-transferase)
 22,582 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Max (Myc-associated factor X) is a basic helix-loop-helix/leucine zipper protein that has been shown to play a central role in the functional activity of c-Myc as a transcriptional activator. Max potentiates the binding of Myc-Max heterodimers through its basic region to its specific E-box Myc site (EMS), enabling c-Myc to transactivate effectively. In addition to the alternatively spliced exon a, several naturally occurring forms of alternatively spliced max mRNAs have been reported, but variant protein products from these transcripts have not been detected. Using Western blot (immunoblot) and immunoprecipitation analysis, we have identified a variant form of Max protein (16 to 17 kDa), termed dMax, in detergent nuclear extracts of murine B-lymphoma cells, normal B lymphocytes, and NIH 3T3 fibroblasts. Cloning and sequencing revealed that dMax contains a deletion spanning the basic region and helix 1 and the loop of the helix-loop-helix region, presumably as a result of alternative splicing of max RNA. S1 nuclease analysis confirmed the presence of the mRNA for dMax in cells. The dMax protein, prepared via in vitro transcription and translation, associated with bacterially synthesized Myc-glutathione S-transferase. Coimmunoprecipitation of dMax and c-Myc indicated their intracellular association. In vitro-synthesized dMax failed to bind EMS DNA, presumably because of the absence of the basic region. Coexpression of dMax inhibited EMS-mediated transactivation by c-Myc. Thus dMax, which can interact with c-Myc, appears to function as a dominant negative regulator, providing an additional level of regulation to the transactivation potential of c-Myc.
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PMID:Variant Max protein, derived by alternative splicing, associates with c-Myc in vivo and inhibits transactivation. 852 35

The c-Myc protein, the product of the c-myc protooncogene, is a nuclear phosphoprotein with DNA-binding properties when heterodimerized with the Max protein. It contains an amino-terminal transcriptional activation domain and a carboxy-terminal basic helix-loop-helix leucine zipper (bHLHzip) domain that directs heterodimerization and promotes DNA binding. Here, we describe the isolation of the bHLHzip domain of human c-Myc with a technique for efficient single-step purification. Using a C-terminal Strep-tag II affinity peptide and a novel Streptactin-Sepharose matrix, elution is performed under mild conditions by competition with the biotin analog desthiobiotin. No significant influence of the affinity tag on the activity of the bHLHzip domain was observed when the fusion protein was subjected to glutathione S-transferase (GST) pull-down assays for investigating its in vitro-binding properties with GST-Max. The use of the C-terminal Strep-tag II was shown to be more suitable for obtaining pure product fractions than use of the N-terminal GST affinity tag.
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PMID:Strep-tag II for one-step affinity purification of active bHLHzip domain of human c-Myc. 1045 46

Mxi1 protein is a basic helix-loop-helix, leucine zipper (bHLHZIP) transcriptional factor, which dimerizes with the Max protein. This heterodimer binds a specific DNA sequence (E-box) and suppresses transcription of target genes. On the other hand, c-Myc protein is also a bHLHZIP protein that dimerizes with Max, binds the identical E-box sequence but activates transcription of the target genes. We report that hematopoietic cells have three novel Mxi1 transcripts: Mxi-D lacks exon 3, which encodes the basic region; Mxi-ND lacks the N-terminal mSin3 binding region and the DNA binding region; and Mxi-NF lacks the N-terminal mSin3 binding region. In normal bone marrow and hematological cell lines, the dominantly expressed isoforms are Mxi-D and full-length Mxi1 (Mxi-F). In GST-pull down assays, the Mxi-D protein binds the Max protein and the PHA2 regions of mSin3 proteins. Whereas the Mxi-F/Max heterodimer binds the E-box sequence, Mxi-D/Max heterodimer can not bind this sequence in electrophoretic mobility shift assays. In reporter gene assay, Mxi-D suppresses transcription as strongly as Mxi-F. In colony formation assay using Rat1 fibroblast cells, Mxi-D cannot suppress clonal growth stimulated by c-Myc as strongly as Mxi-F. In summary, Mxi-D may play an important role in the c-Myc family protein network acting as a dominant negative isoform of Mxi-F since: i) Mxi-D can dimerize with Max in vitro; ii) Mxi-D/Max heterodimers cannot bind E-box in vitro, iii) Mxi-D cannot suppress clonal growth stimulated by c-Myc.
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PMID:Mxi1 isoforms are expressed in hematological cell lines and normal bone marrow. 1580 30