Rat Rev-erbA alpha, an orphan receptor related to thyroid hormone receptor, binds to specific thyroid hormone...

Rat Rev-erbA alpha (rRev), which is related to thyroid hormone receptor (TR), is a conserved member of the nuclear hormone receptor superfamily whose physiological roles are unknown ("orphan" receptor). We studied DNA binding of rRev in vitro by electrophoretic mobility shift assay. A fusion protein was constructed, called NGR.Rev, containing part of the N terminus of the glucocorticoid receptor fused to nearly full-length rRev. Inasmuch as rRev and TR share homology in their DNA-binding domains, we tested binding to three different thyroid hormone response elements (TREs) in which the half-sites are arranged in different orientations. NGR.Rev bound direct repeats (DR4), but not palindromic (TREpal) or inverted palindromic (F2H) repeats. Also, transfection of CV1 cells with a reporter gene containing the luciferase gene under control of the inducible thymidine kinase promoter resulted in an increase in luciferase activity when NGR.Rev was cotransfected and when the thymidine kinase promoter contained DR4. In addition, a series of deletions in the ligand-binding domain of NGR.Rev revealed regions that can modulate DNA binding. Finally, we studied DNA binding of bacterially produced fusion proteins that contain the DNA-binding domains of rRev or rTR alpha fused to glutathione S-transferase, to a panel of natural TREs. Our results indicate that Rev binds DNA with a different specificity than TR alpha-1 and might be involved in the regulation of a subset of thyroid hormone-regulated genes.