Structure and function of CRSP/Med2; a promoter-selective transcriptional coactivator complex.
The multi-subunit, human CRSP coactivator-also known as Mediator (Med)-regulates transcription by mediating signals between enhancer-bound factors (activators) and the core transcriptional machinery. Interestingly, different activators are known to bind distinct subunits within the CRSP/Med complex. We have isolated a stable, endogenous CRSP/Med complex (CRSP/Med2) that specifically lacks both the Med220 and the Med70 subunits. The three-dimensional structure of CRSP/Med2 was determined to 31 A resolution using electron microscopy and single-particle reconstruction techniques. Despite lacking both Med220 and Med70, CRSP/Med2 displays potent, activator-dependent transcriptional coactivator function in response to VP16, Sp1, and Sp1/SREBP-1a in vitro using chromatin templates. However, CRSP/Med2 is unable to potentiate activated transcription from a vitamin D receptor-responsive promoter, which requires interaction with Med220 for coactivator recruitment, whereas VDR-directed activation by CRSP/Med occurs normally. Thus, it appears that CRSP/Med may be regulated by a combinatorial assembly mechanism that allows promoter-selective function upon exchange of specific coactivator targets.
Taatjes
Dylan J
DJ
Howard Hughes Medical Institute, Department of Molecular and Cell Biology, 401 Barker Hall, University of California-Berkeley, Berkeley, CA 94720, USA.
Tjian
Robert
R
D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005809:Genes, Regulator / Q000235:genetics*; D006367:HeLa Cells; D017405:Herpes Simplex Virus Protein Vmw65 / Q000235:genetics / Q000378:metabolism; D006801:Humans; D046911:Macromolecular Substances; D011401:Promoter Regions, Genetic / Q000235:genetics*; D017434:Protein Structure, Tertiary / Q000502:physiology; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism; D051780:Sterol Regulatory Element Binding Protein 1; D015534:Trans-Activators / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors; D015533:Transcriptional Activation / Q000235:genetics*; D030181:Vitamin D Response Element / Q000235:genetics
D022762:CCAAT-Enhancer-Binding Proteins; C117286:CRSP protein, human; D004268:DNA-Binding Proteins; D017405:Herpes Simplex Virus Protein Vmw65; D046911:Macromolecular Substances; D021122:Protein Subunits; C497387:SREBF1 protein, human; D016329:Sp1 Transcription Factor; D051780:Sterol Regulatory Element Binding Protein 1; D015534:Trans-Activators; D014157:Transcription Factors