Active repression and E2F inhibition by pRB are biochemically distinguishable.
To understand mechanistically how pRB represses transcription, we used a reconstituted transcription assay and compared pRB activity on naked versus chromatin templates. Surprisingly, when pRB was directly recruited to a naked template, no transcriptional repression was observed. However, we observed active repression when the same promoter was assembled into chromatin. Histone deacetylases do not appear to play a role in this observed repression. Further experiments showed repression could occur after preinitiation complex assembly, in contrast with pRB inhibition of E2F, suggesting discrete mechanisms by which pRB directly inhibits an activator such as E2F or actively represses proximally bound transcription factors.
Harvard University, Department of Molecular and Cellular Biology, Cambridge, Massachusetts 02138, USA.
J F
JF
Ross
A
A
Näär
H
H
Cam
R
R
Gregory
B D
BD
Dynlacht
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D006655:Histone Deacetylases / Q000378:metabolism; D006801:Humans; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000502:physiology*; D016160:Retinoblastoma Protein / Q000502:physiology*; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000037:antagonists & inhibitors*; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D006655:Histone Deacetylases