Active repression mechanisms of eukaryotic transcription repressors

Regulators of transcription and, in particular, transcriptional repressors, play central roles in vital biological processes, such as development and the regulation of cell growth. A major class of transcriptional repressors consists of DNA-binding proteins that interact with specific promoter elements and repress transcription via small, portable repression 'domains'. Such transcriptional inhibition, first identified only five years ago, has been termed active repression, because it is not mediated simply by steric hindrance mechanisms. It is unknown how interaction(s) between such a repressor and the RNA polymerase II basal or regulatory transcription machinery can derail the formation or competency of a transcription complex at a promoter. However, the recent progress toward identification of molecular targets suggests several specific mechanisms for achieving active repression.