Regulating the Regulon

Science Signaling  26 Feb 2008:
Vol. 1, Issue 8, pp. ec76
DOI: 10.1126/stke.18ec76

In the presence of galactose, the yeast Saccharomyces cerevisiae transports the sugar into its cytoplasm, where the galactose binds the Gal3 protein, which in turn sequesters the Gal80 repressor away from the transcriptional activator Gal4, resulting in the induction of galactose-metabolizing enzymes. The induction is so rapid that it has been suggested that another unknown factor must somehow be involved in this "galactose regulon." Kumar et al. have identified this factor as nicotinamide adenine dinucleotide (NAD) and its phosphate (NADP). In the Gal4:Gal80 complex, NAD is sandwiched between the two proteins. NADP, on the other hand, inhibits the interaction between Gal4 and Gal80. Mutations that have the potential to affect the NAD-binding site in Gal80 result in even faster induction, which suggests that Gal80 is sensing the balance between NAD and NADP and thus the metabolic state of the cell.

P. R. Kumar, Y. Yu, R. Sternglanz, S. A. Johnston, L. Joshua-Tor, NADP regulates the yeast GAL induction system. Science 319, 1090-1092 (2008). [Abstract] [Full Text]