Transcriptional repression in eukaryotes: repressors and repression mechanisms.

For many, if not most genes, the initiation of transcription is the principle point at which their expression is regulated. Transcription factors, some of which bind to specific DNA sequences, generally either activate or repress promoter activity and thereby control transcription initiation. Recent work has revealed in molecular detail some of the mechanisms used by transcription factors to bring about transcriptional repression. Some transcriptional repressor proteins counteract the activity of positively acting transcription factors. Other repressors inhibit the basal transcription machinery. In addition, the repression of transcription is often intimately associated with chromatin re-organisation. Many transcriptional repressor proteins interact either directly or indirectly with proteins that remodel chromatin or can themselves influence chromatin structure. This review discusses the mechanisms by which transcriptional repression is achieved and the role that chromatin re-organisation plays in this process.