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Mol. Cell. Biol., Mar 1995, 1499-1512, Vol 15, No. 3
R Uppaluri and HC Towle
The thyroid hormone receptors (TR) are members of the nuclear receptor
family of ligand-mediated transcription factors. The large region of TR
that lies C-terminal to its DNA-binding domain subserves functions of
ligand binding, dimerization, and transactivation. Little is known
regarding the structural or functional determinants of these processes. We
have utilized genetic screening in the yeast Saccharomyces cerevisiae to
identify residues involved in these functions. Random mutations of the rat
TR beta 1 isoform between amino acid residues 179 and 456 were screened,
and mutants with reduced hormone-dependent activation of reporter gene
activity were isolated. In this paper we describe the characterization of a
class of mutants that exhibit a dissociation between hormone binding and
transcriptional activation. These mutants retained hormone binding (>
15% of the wild-type level) yet failed to transactivate a reporter gene. A
number of these mutations occurred within the D region, which links the
DNA-binding and ligand-binding domains of the receptor. One subset of these
mutations abrogated DNA binding, supporting a role of the D region in this
process. The remainder retain DNA binding and thus highlight residues
critical for receptor activation. In addition, an unexpected group of
"superactivator" mutations that led to enhanced hormone-dependent
activation in S. cerevisiae were found. These mutations localized to the
carboxy-terminal portion of the receptor in a region which contains
elements conserved across the superfamily of nuclear receptors. The
hormone-dependent phenotype of these superactivator mutations suggests an
important role of this segment in ligand-mediated transcriptional
activation.
Copyright © 1995, American Society for Microbiology
Genetic dissection of thyroid hormone receptor beta: identification of mutations that separate hormone binding and transcriptional activation
Department of Biochemistry, University of Minnesota, Minneapolis 55455.
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