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Mol. Cell. Biol., Sep 1995, 4791-4802, Vol 15, No. 9
HP Harding and MA Lazar
Rev-Erb is an orphan nuclear receptor which binds as a monomer to the
thyroid/retinoic acid receptor half-site AGGTCA flanked 5' by an A/T- rich
sequence, referred to here as a Rev monomer site. Fusion of Rev- Erb to the
DNA binding domain of yeast GAL4 strongly repressed basal transcription of
a GAL4-luciferase reporter gene as a result of the presence of a C-terminal
domain containing both the hinge and heptad repeat regions. Nevertheless,
wild-type Rev-Erb did not repress basal transcription from the Rev monomer
binding site. Therefore, a DNA binding site selection strategy was devised
to test the hypothesis that Rev-Erb may function on a different site as a
dimer. This approach identified sequences containing two Rev monomer sites
arranged as direct repeats with the AGGTCA motifs separated by 2 bp
(Rev-DR2). Remarkably, Rev-Erb bound as a homodimer to Rev-DR2 but not to
other direct repeats or to a standard DR2 sequence. The DNA binding domain
contained all of the determinants for Rev-DR2-specific homodimerization.
Rev-Erb bound cooperatively as a homodimer to Rev- DR2, and this
interaction was 5 to 10 times more stable than Rev-Erb monomer binding to
the Rev monomer site. Functionally, Rev-Erb markedly repressed the basal
activity of a variety of promoters with a strong Rev-DR2 specificity. The C
terminus was required for this repression, consistent with the GAL4
results. However, the Rev-DR2 specificity did not require the C terminus in
vivo, since fusion of C-terminally truncated Rev-Erb to a heterologous
transactivation domain created a transcriptional activator specific for
Rev-DR2. In addition to idealized Rev-DR2 sites, Rev-Erb also repressed
basal as well as retinoic acid-induced transcription from a naturally
occurring Rev-DR2 in the CRBPI gene. Thus, although Rev-Erb is
distinguished from other thyroid/steroid receptor superfamily members by
its ability to bind DNA as a monomer, it functions as a homodimer to
repress transcription of genes containing a novel DR2 element.
Copyright © 1995, American Society for Microbiology
The monomer-binding orphan receptor Rev-Erb represses transcription as a dimer on a novel direct repeat [published erratum appears in Mol Cell Biol 1995 Nov;15(11):6479]
Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104, USA.
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