Functional characterization of a mutant thyroid hormone receptor in Xenopus laevis.

The Journal of Biological Chemistry
M Puzianowska-KuznickaY B Shi

Abstract

Thyroid hormone plays a causative role during frog metamorphosis, and its effect is mediated by thyroid hormone receptors (TRs). To investigate the function of Xenopus TRs, we have recently developed a thyroid hormone dependent in vivo transcription system by introducing TRs and RXRs (9-cis-retinoic acid receptors) into Xenopus oocytes. Interestingly, using this system, we have found that the TRalphaB cloned previously is defective in transcriptional activation compared with TRalphaA. In vitro DNA binding experiments show that TRalphaB.RXR heterodimers have drastically reduced affinity for a thyroid hormone response element. Site-directed mutagenesis shows that two of the seven amino acid residues that differ between TRalphaA and TRalphaB are responsible for the defect in TRalphaB function. These two residues affect the DNA binding by both TR.RXR heterodimers and TR homodimers. In contrast, heterodimer formation with RXRs is not affected as demonstrated by coimmunoprecipitation and dominant-transcriptional inhibition experiments. By cDNA and genomic DNA sequence analysis, we have demonstrated that the residues, which affect TRalphaB function when mutated, are identical between the wild type TRalphaB and TRalphaA. Thus, our expe...Continue Reading

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Nov 28, 2008·Developmental Dynamics : an Official Publication of the American Association of Anatomists·Rachel C SkirrowCaren C Helbing
Oct 26, 2005·BMC Developmental Biology·Elena LazakovitchRichard M Gronostajski

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