CSL: A notch above the rest

CSL (CBF1, Suppressor of Hairless, Lag-1) is a transcription factor that is responsible for activating the genes downstream of the Notch signalling pathway, a pathway that is essential for the development of the nervous system and the differentiation of the haematopoietic system among others. In the absence of Notch signalling, CSL represses transcription of Notch target genes, and following activation by Notch, CSL is converted into a transcriptional activator and activates transcription of the same genes. These two opposing functions of CSL are mediated through interactions with distinct protein complexes. The Notch signalling pathway and its crucial cofactor CSL can maintain cells in an undifferentiated state, and have therefore been associated with a growing list of cancers. In addition, CSL has been co-opted by Epstein-Barr virus to mediate viral and host gene transcription following infection.