Factors influencing nuclear receptors in transcriptional repression.

Members of the steroid receptor superfamily, like other transcription factors, can function as transcriptional inducers as well as repressors of transcription. The mechanisms by which repression is achieved seem to be specific for the factors and regulatory sequences involved. Silencing activity is conferred by the DNA bound v-ERBA, which is able to repress the activity of a complete or of a minimal promoter. Removal of the T3 or RA ligands converts the activated form of TR or RAR into a silencing conformation. Ligand-free TR, RAR or v-ERBA synergize with the DNA-bound negative protein 1 (NeP1) in a specific silencer sequence. In contrast to silencing, competitive repression is seen for specific negative hormone response elements. These elements are characterized by the presence of binding sites for other transcription factors.