RARs (α，β, and γ and their isoforms) and RXRs (α，β, and γ and their isoforms) are members of the nuclear receptor superfamily. They act as ligand-activated transcriptional regulators transducing the RA signal and then control the expression of target genes.
RARs bind to all-trans RA (T-RA) and 9-cis RA. Whereas RXRs only bind to 9-cis RA. RAR/RXR heterodimers bind much more efficiently than the respective homodimers to RA response elements (RAREs). There exists some evidence that supports this conclusion, especially in vitro studies with isolated receptors or cells RAR/RXR expression vectors. RXR may acts as a silent partner when the heterodimer binds to a DR5 response element.
Moreover, both RAR and RXR partners of RAR/RXR heterodimers can bind to ligands. And then, they activate to induce synergistically the expression of a variety of RA target genes.
There are three divergent amino acid residues in the ligand-binding pockets (LBPs) of RARα, RARβ, and RARγ.

And 3 kinds of retinoid agonists and antagonists have been researched. The monospecific (class I) retinoid agonists and antagonists bind to and induce or inhibit transactivation by a given isotype that directly links to the nature of these residues. The class II retinoids, which bind to all three RARs but depending on the RAR isotype.

In this article, we will introduce an isotype- selective retinoic acid receptor α (RARα) agonist, BMS 753.

BMS 753 results in low levels of RARβ transcripts in WT cells, RARγ-/-, but not activates in RARa-/- cells.  The specific RAR agonist, BMS 753, acting either alone or synergistically with a pan- RXR-agonist.

BMS 753 is more restricted than T-RA in its effects on both RA target gene expression and morphological differentiation of EC cells. Additionally, the antagonist characteristics of retinoids are not conserved in yeast cells. this suggests that yeast co-regulators interact with RARs in a different way than the animal cell homologs do.

Reference:

[1]. M Géhin, et al. Chem Biol. 1999 Aug;6(8):519-29.