Regulation of transcription: from lambda to eukaryotes

• Published in: Trends in biochemical sciences (Amsterdam. Regular ed.) 2005-06, Vol.30 (6), p.275-278
• Main Author: Ptashne, M
• Format: Article
• Language: English
• ISSN: 0968-0004
• DOI: 10.1016/j.tibs.2006.04.011

In the late 1960s, it seemed desperately important to isolate and determine the mode of action of repressors, and so we did, and they turned out to be proteins that bind to specific sites on DNA and block binding of RNA polymerase. Each repressor is inactivated, and its target gene turned on, by a specific environmental signal: the lac repressor by the sugar lactose, and the lambda repressor by UV irradiation. Repression seemed to be all we needed. It emerged, however, that, in the absence of its repressor, the typical bacterial gene (including lac) is expressed only at a low level - the basal level - unless stimulated by an 'activator'. And early explorations of gene control in eukaryotes were difficult to reconcile with a repressor-dominated world. Transcription of the Gal (galactose utilization) genes of yeast, for example, is dramatically increased by Gal4, a protein that binds specific DNA sites and, in the presence of galactose, activates the nearby Gal genes. The lambda repressor itself, named because of its ability to turn off transcription of certain phage genes, also turned out to be an activator of transcription of it shown gene.