Molecular and Cellular Biology, August 1999, p. 5486-5494, Vol. 19, No. 8
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, Illkirch Cédex, C.U. de Strasbourg, France
Received 9 October 1998/Returned for modification 14 December 1998/Accepted 14 May 1999
We have identified novel interactions between the human
(h)TATA-binding protein-associated factor TAFII55 and the
ligand-binding domains (LBDs) of the nuclear receptors for vitamin
D3 (VDR) and thyroid hormone (TR
). Following expression
in Cos cells, hTAFII55 interacts with the VDR and TR
LBDs in a ligand-independent manner whereas no interactions with the
retinoid X receptors (RXRs) or with other receptors were observed.
Deletion mapping indicates that hTAFII55 interacts with a
40-amino-acid region spanning
-helices H3 to H5 of the VDR and TR
LBDs but not with the equivalent highly related region of RXR
.
TAFII55 also interacts with chimeric receptors in which the
H3-to-H5 region of RXR
has been replaced with that of the VDR or
TR
. Furthermore, replacement of two single amino acids of the RXR
LBD with their VDR counterparts allows the RXR
LBD to interact with
hTAFII55 while the corresponding double substitution allows
a much stronger interaction. In transfection experiments, the single
mutated RXR
LBDs activate transcription to fivefold higher levels
than wild-type RXR
while the double mutation activates transcription
to a level comparable to that observed with the VDR. There is therefore
a correlation between the ability of the modified RXRs to interact with
hTAFII55 and transactivation. These results strongly
suggest that the TAFII55 interactions with the modified RXR
LBDs modulate transcriptional activation.
Present address: EMBL, 69012, Heidelberg, Germany.
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