Sk. Lee et al., IDENTIFICATION OF CRITICAL RESIDUES FOR HETERODIMERIZATION WITHIN THELIGAND-BINDING DOMAIN OF RETINOID-X-RECEPTOR, Molecular endocrinology, 12(3), 1998, pp. 325-332
Nuclear receptors regulate transcription by binding to specific DNA re
sponse elements as homodimers or heterodimers with the retinoid X rece
ptors (RXRs), The identity box (I-box), a 40-amino acid region within
the ligand-binding domains of RXRs and other nuclear receptors, was re
cently shown to determine identity in the heterodimeric interactions.
Here, we dissected this region in the yeast two-hybrid system by analy
zing a series of chimeric receptors between human RXR alpha and rat he
patocyte nuclear factor 4 (HNF4), a distinct member of the nuclear rec
eptor superfamily that prefers homodimerization, We found that the C-t
erminal Il-amino acid region of the RXR I-box was sufficient to direct
chimeric receptors based on the HNF4 ligand-binding domain to heterod
imerize with retinoic acid receptors or thyroid hormone receptors. Fur
thermore, we identified the hRXR alpha amino acids A416 and R421 of th
e Il-amino acid subregion as most critical determinants of heterodimer
ic interactions; i.e. mutant HNF4s incorporating only the hRXR alpha A
416 or R421 heterodimerized with retinoic acid receptor.