Does the transactivation function of the ligand binding domain interfere with functionality?
The ligand binding domain of most nuclear receptors contains a transactivation function, termed TAF-2. This can certainly be a problem when the hbd is attached to a weak transactivator (Schuermann et al., 1993). A current technique to test the requirement for transcriptional regulators in gene expression is to fuse the repressor region of the Drosophila engrailed protein (EnR) (Jaynes and O’Farrell, 1991) to the DNA binding domain of the transcriptional activator to be examined (Conlon et al., 1996; Fan and Sokol, 1997). Addition of a strong activation domain could cancel out the repressor activity of these proteins. This problem could be prevented by using mutant forms of GR or ER that inactivate the TAF-2 activity (Mattioni et al., 1994; Lyon and Watson, 1996). Indeed, tamoxifen-inducible ER that does not have TAF-2 function has been shown to effectively regulate the activity of a Myb-EnR fusion protein (Lyon and Watson, 1996).
