Figure 5. TH receptor-mediated transcriptional silencing and activation. (A) Positively regulated genes. In the absence of hormone, the unliganded TH receptor represses or “silences” transcription in a process that involves TR interactions with a corepressor complex. Binding of T3 releases corepressors, relieving silencing and inducing the recruitment of coactivators that mediate transcriptional stimulation. (B) Negatively regulated genes. In the absence of hormone, the unliganded receptor activates transcription in a process that involves corepressors. Addition of TH dissociates corepressors and recruits coactivators. In the case of negatively regulated genes, this T3-mediated exchange of corepressors and coactivators inhibits transcription.