The alpha chain of the nascent polypeptide-associated complex functions as a transcriptional coactivator.
We report the characterization of clone 1.9.2, a gene expressed in mineralizing osteoblasts. Remarkably, clone 1.9.2 is the murine homolog of the alpha chain of the nascent polypeptide-associated complex (alpha-NAC). Based on sequence similarities between alpha-NAC/1.9.2 and transcriptional regulatory proteins and the fact that the heterodimerization partner of alpha-NAC was identified as the transcription factor BTF3b (B. Wiedmann, H. Sakai, T. A. Davis, and M. Wiedmann, Nature 370:434-440, 1994), we investigated a putative role for alpha-NAC/ 1.9.2 in transcriptional control. The alpha-NAC/1.9.2 protein potentiated by 10-fold the activity of the chimeric activator GAL4/VP-16 in vivo. The potentiation was shown to be mediated at the level of gene transcription, because alpha-NAC/1.9.2 increased GAL4/VP-16-mediated mRNA synthesis without affecting the half-life of the GAL4/VP-16 fusion protein. Moreover, the interaction of alpha-NAC/1.9.2 with a transcriptionally defective mutant of GAL4/VP-16 was severely compromised. Specific protein-protein interactions between alpha-NAC/1.9.2 and GAL4/VP-16 were demonstrated by gel retardation, affinity chromatography, and protein blotting assays, while interactions with TATA box-binding protein (TBP) were detected by immunoprecipitation, affinity chromatography, and protein blotting assays. Based on these interactions that define the coactivator class of proteins, we conclude that the alapha-NAC/1.9.2 gene product functions as a transcriptional coactivator.
Yotov
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WV
Shriners Hospital, and Department of Surgery, McGill University, Montréal, Québec, Canada.
Moreau
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A
St-Arnaud
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R
D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins; D017405:Herpes Simplex Virus Protein Vmw65 / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018832:Molecular Chaperones; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016192:Resting Phase, Cell Cycle; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D035362:Transcription Factor TFIID; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D019473:Transcription Factors, TFII / Q000378:metabolism; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; C052130:GAL4 protein, S cerevisiae; D017405:Herpes Simplex Virus Protein Vmw65; D018832:Molecular Chaperones; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D035362:Transcription Factor TFIID; D014157:Transcription Factors; D019473:Transcription Factors, TFII; C096099:nascent-polypeptide-associated complex