Transcription factors: bound to activate or repress

The complex processes of eukaryotic gene expression are controlled by a rel atively small number of transcription factors whose activities are modulate d by a diverse set of regulatory mechanisms. A recent paper describes the m olecular basis for one such mechanism in which the Pit-1 transcription fact or activates or represses transcription depending on the sequence of the DN A to which it binds. The mechanism by which the binding-site sequence regul ates the activity of Pit-1 is discussed in relation to that of other transc ription factors.