RECONSTITUTION OF THYROID-HORMONE RECEPTOR AND RETINOIC ACID RECEPTOR FUNCTION IN THE FISSION YEAST SCHIZOSACCHAROMYCES-POMBE

We report here a characterization of the thyroid hormone receptors (T(3)Rs), retinoic acid receptors (RARs), and retinoid X receptors (RXRs) by reconstituting their actions in the fission yeast Schizosaccharomyces pombe. S. pombe provide a well defined and readily manipulated genetic background devoid of known endogenous nuclear hormone receptors. All the receptors tested, when introduced exogenously into S. pombe, induced high levels of reporter gene activation in response to physiological concentrations of hormone ligand. In these properties, the S. pombe system exhibits significant advantages over the previously employed Saccharomyces cerevisiae system. Use of the S. pombe system permitted the elucidation of previously undescribed differences in the DNA sequence recognition properties of different isoforms of the RXR and RARs, and the identification of apparently novel forms of response element for RXRs and RARs. Intriguingly, the v-erb A allele of T(3)R, a transcriptional repressor in vertebrate cells, acts as a transcriptional activator both in S. cerevisiae and in the evolutionarily highly divergent S. pombe, underscoring the importance of cellular factors in the regulation of receptor transcriptional activity.