Transcription coactivators and corepressors acting as bridges. Coactivators and corepressors act indirectly, binding regulatory proteins without making direct contact with DNA. (a) Coactivators bind transcription activators and facilitate their function in activating RNA polymerase. (b) Corepressors bind transcription activators and inactivate their polymerase-activating function. In these examples, the activators are bound upstream from the promoter, but activator sites can also be located downstream.