Multiple forms of C/EBPβ bind the EFII enhancer sequence in the rous sarcoma virus long terminal repeat

Rosalie C. Sears, Linda Sealy

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48 Scopus citations


In this report we demonstrate that C/EBPβ is a major component of three EFII DNA binding complexes, EFIIa, EFIIb, and EFIIc, which we have previously shown to specifically recognize a C/EBP consensus binding site found in the EFII enhancer sequence from the Rous sarcoma virus long terminal repeat (R. C. Sears and L. Sealy, J. Virol. 66:6338-6352, 1992). Three different forms of C/EBPβ, p42, p35, and p20, can bind the EFII DNA sequence as homodimers, and dimerization experiments show that EFIIa is a homodimer of p20 C/EBPβ, EFIIb is primarily composed of a p20/p35 heterodimer with minor amounts of p20/p42 heterodimer and p35 homodimer, and EFIIc is composed of p20 and/or p35 heterodimerized with a novel 60-kDa protein. p20 C/EBPβ is likely equivalent to the internally initiated translation product of C/EBPβ, LIP (liver inhibitor protein), described by P. Descombes and U. Schibler (Cell 67:569-579, 1991). In contrast to the low level of LIP expressed in liver, postulated to occur because of leaky ribosome scanning, we found high levels of expression of p20 C/EBPβ in fibroblasts and lymphocytes. In murine fibroblasts, p20 C/EBPβ has an extended half-life, four times longer than those of p42 and p35 C/EBPβ, which could contribute to its abundant accumulation in this cell type, even though its synthesis by leaky ribosome scanning might be inefficient. Interestingly, overexpression of either the long or short form of C/EBPβ represses EFII-mediated transcription, suggesting that another unidentified EFII transactivator(s) exists, which may be dominantly inhibited by C/EBPβ proteins, and/or that transactivation by C/EBPβ proteins requires posttranslational modifications that were lacking in the transient overexpression experiments.

Original languageEnglish (US)
Pages (from-to)4855-4871
Number of pages17
JournalMolecular and cellular biology
Issue number7
StatePublished - Jul 1994
Externally publishedYes

ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology


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