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Mol. Cell. Biol., 05 1995, 2517-2526, Vol 15, No. 5
V Giguere, LD McBroom and G Flock
The ROR alpha isoforms are orphan members of the steroid/thyroid/retinoid
receptor superfamily. Previous DNA-binding studies indicated that ROR alpha
isoforms bind to response elements consisting of a single copy of the core
recognition sequence AGGTCA preceded by a 6-bp A/T-rich sequence and that
the distinct amino- terminal domains of each isoform influence DNA-binding
specificity. In this report, we have investigated in detail the protein
determinants of target gene specificity for the ROR alpha 1 isoform and
have now identified the minimal sequence both in its amino- and
carboxy-terminal domains required for high-affinity DNA binding.
High-resolution methylation and ethylation interference analyses and mixing
of truncated proteins in a DNA-binding assay show that ROR alpha 1
presumably binds along one face of the DNA helix as a monomer. By analogy
to previous studies of the orphan receptors NGFI-B and FTZ-F1, extensive
mutational analysis of the ROR alpha 1 protein shows that a domain
extending from the carboxy-terminal end of the second conserved
zinc-binding motif is required for specific DNA recognition. However, point
mutations and domain swap experiments between ROR alpha 1 and NGFI-B
demonstrated that sequence-specific recognition dictated by the
carboxy-terminal extension is determined by distinct subdomains in the two
receptors. These results demonstrate that monomeric nuclear receptors
utilize diverse mechanisms to achieve high-affinity and specific DNA
binding and that ROR alpha 1 represents the prototype for a distinct
subfamily of monomeric orphan nuclear receptors.
Copyright © 1995, American Society for Microbiology
Determinants of target gene specificity for ROR alpha 1: monomeric DNA binding by an orphan nuclear receptor
Molecular Oncology Group, Royal Victoria Hospital, Montreal, Quebec, Canada.
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