Modification of chromatin structure by the thyroid hormone receptor

Pioneering experiments and recent observations have established the thyroid hormone receptor as a master manipulator of the chromosomal environment in targeting the activation and repression of transcription. Here we review h ow the thyroid hormone receptor is assembled into chromatin, where in the a bsence of thyroid hormone the receptor recruits histone deacetylase to sile nce transcription. On addition of hormone, the receptor undergoes a conform ational change that leads to the release of deacetylase, while facilitating the recruitment of transcriptional coactivators that act as histone acetyl transferases. We discuss the biological importance of these observations fo r gene control by the thyroid hormone receptor and Ibr oncogenic transforma tion by the mutated thyroid hormone receptor v-ErbA.