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Mol. Cell. Biol., 02 1995, 796-808, Vol 15, No. 2
LD McBroom, G Flock and V Giguere
ROR alpha 1 and ROR alpha 2 are two isoforms of a novel member of the
steroid-thyroid-retinoid receptor superfamily and are considered orphan
receptors since their cognate ligand has yet to be identified. These
putative receptors have previously been shown to bind as monomers to a DNA
recognition sequence composed of two distinct moieties, a 3' nuclear
receptor core half-site AGGTCA preceded by a 5' AT-rich sequence.
Recognition of this bipartite hormone response element (RORE) requires both
the zinc-binding motifs and a group of amino acid residues located at the
carboxy-terminal end of the DNA-binding domain (DBD) which is referred to
here as the carboxy-terminal extension. In this report, we show that
binding of ROR alpha 1 and ROR alpha 2 to the RORE induces a large DNA bend
of approximately 130 degrees which may be important for receptor function.
The overall direction of the DNA bend is towards the major groove at the
center of the 3' AGGTCA half-site. The presence of the nonconserved hinge
region which is located between the DBD and the putative ligand-binding
domain (LBD) or ROR alpha is required for maximal DNA bending. Deletion of
a large portion of the amino-terminal domain (NTD) of the ROR alpha protein
does not alter the DNA bend angle but shifts the DNA bend center 5'
relative to the bend induced by intact ROR alpha. Methylation interference
studies using the NTD-deleted ROR alpha 1 mutant indicate that some DNA
contacts in the 5' AT-rich half of the RORE are also shifted 5', while
those in the 3' AGGTCA half-site are unaffected. These results are
consistent with a model in which the ROR alpha NTD and the nonconserved
hinge region orient the zinc-binding motifs and the carboxy-terminal
extension of the ROR alpha DBD relative to each other to achieve proper
interactions with the two halves of its recognition site. Transactivation
studies suggest that both protein-induced DNA bending and protein-protein
interactions are important for receptor function.
Copyright © 1995, American Society for Microbiology
The nonconserved hinge region and distinct amino-terminal domains of the ROR alpha orphan nuclear receptor isoforms are required for proper DNA bending and ROR alpha-DNA interactions
Department of Biochemistry, McGill University, Royal Victoria Hospital, Montreal, Quebec, Canada.
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