Abstract
The human cofactor complexes ARC (activator-recruited cofactor) and CRSP (cofactor required for Sp1 activation) mediate activator-dependent transcription in vitro. Although these complexes share several common subunits, their structural and functional relationships remain unknown. Here, we report that affinity-purified ARC consists of two distinct multisubunit complexes: a larger complex, denoted ARC-L, and a smaller coactivator, CRSP. Reconstituted in vitro transcription with biochemically separated ARC-L and CRSP reveals differential cofactor functions. The ARC-L complex is transcriptionally inactive, whereas the CRSP complex is highly active. Structural determination by electron microscopy (EM) and three-dimensional reconstruction indicate substantial differences in size and shape between ARC-L and CRSP. Moreover, EM analysis of independently derived CRSP complexes reveals distinct conformations induced by different activators. These results suggest that CRSP may potentiate transcription via specific activator-induced conformational changes.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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CCAAT-Enhancer-Binding Proteins / chemistry
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CCAAT-Enhancer-Binding Proteins / metabolism
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Chromatin / metabolism
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DNA-Binding Proteins / chemistry
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DNA-Binding Proteins / metabolism
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HeLa Cells
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Herpes Simplex Virus Protein Vmw65 / metabolism
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Humans
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Image Processing, Computer-Assisted
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Imaging, Three-Dimensional
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Macromolecular Substances
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Microscopy, Electron
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Models, Genetic
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Precipitin Tests
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Protein Binding
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Protein Structure, Quaternary
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Protein Structure, Tertiary
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Protein Subunits
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Recombinant Fusion Proteins / chemistry
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Recombinant Fusion Proteins / metabolism
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Recombinant Proteins / metabolism
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Sterol Regulatory Element Binding Protein 1
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Trans-Activators / chemistry*
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Trans-Activators / isolation & purification
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Trans-Activators / metabolism*
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Transcription Factors / metabolism
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Transcription, Genetic*
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Transcriptional Activation
Substances
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CCAAT-Enhancer-Binding Proteins
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CRSP protein, human
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Chromatin
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DNA-Binding Proteins
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Herpes Simplex Virus Protein Vmw65
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Macromolecular Substances
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Protein Subunits
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Recombinant Fusion Proteins
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Recombinant Proteins
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SREBF1 protein, human
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Sterol Regulatory Element Binding Protein 1
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Trans-Activators
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Transcription Factors