The transcription factor CCAAT/enhancer binding protein α (C/EBPα) is the DNA binding subunit of a multiprotein complex that regulates the pituitary-specific GH promoter. C/EBPα is absent from the GHFT1-5 pituitary progenitor cell line in which ectopic C/EBPα expression leads to activation of the otherwise dormant GH promoter. Transcriptional regulatory complexes are commonly envisaged as assembling from components that evenly diffuse throughout the nucleoplasm. We show that C/EBPα, expressed in GHFT1-5 cells as a fusion with color variants of the green fluorescent protein (GFP), concentrated specifically at peri-centromeric chromosomal domains. Although we found the CREB-binding protein (CBP) to activate C/EBPα-dependent transcription, CBP was absent from the pericentromeric chromatin. C/EBPα expression was accompanied by the translocation of endogenous and ectopically expressed CBP to pericentromeric chromatin. The intranuclear recruitment of CBP required the transcriptional activation domains of C/EBPα. C/EBPα also caused GFP-tagged TATA binding protein (TBP) to relocate to the Hoechst-stained domains. The altered intranuclear distribution of critical coregulatory factors defines complexes formed upon C/EBPα expression. It also identifies an organizational activity, which we label "intranuclear marshaling," that may regulate gene expression by determining the cooperative and antagonistic interactions available at specific nuclear sites.
ASJC Scopus subject areas
- Molecular Biology