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Mol. Cell. Biol., Aug 1997, 4259-4271, Vol 17, No. 8
A Baniahmad, D Thormeyer and R Renkawitz
Members of the thyroid hormone (TR)-retinoic acid receptor (RAR) subfamily
of nuclear hormone receptors silence gene expression in the absence of
hormone. Addition of cognate ligands leads to dissociation of corepressors,
association of coactivators, and transcriptional activation. Here, we used
the hRAR alpha silencer core, which encompasses the ligand binding domain,
including receptor regions D and E of RAR alpha without the activation
function called tau4/tau c/AF-2 and without the F region, to analyze the
mechanisms by which transcriptional silencing is relieved. Although the RAR
silencer core is able to bind ligand, it acts as a constitutive
transcriptional silencer. We have fused various small activation domains to
the C terminus of the silencer core and analyzed hormone-dependent changes
in receptor function. We show that nine amino acids derived from the
hTRbeta are sufficient to transform the RAR silencer core into a
hormone-dependent activator. Lengthening the linker between the silencer
core and these nine amino acids is not critical for mediating
ligand-induced relief of silencing and activation. In addition, we show
that a transactivation function at the C terminus is not required for
relief of silencing by the hormone, but it is required for transcriptional
activation. Furthermore, we created functional silencer fusions which lose
their repressive function upon addition of hormone, although the
corepressors SMRT and N-CoR remain attached to the receptor.
Copyright © 1997, American Society for Microbiology
tau4/tau c/AF-2 of the thyroid hormone receptor relieves silencing of the retinoic acid receptor silencer core independent of both tau4 activation function and full dissociation of corepressors
Genetisches Institut der Justus-Liebig Universitat, Giessen, Germany. Aria.Baniahmad@Gen.Bio.Uni-Giessen.de
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