STRUCTURE FUNCTION PROPERTIES OF THE YEAST DUAL REGULATOR PROTEIN NGG1 THAT ARE REQUIRED FOR GLUCOSE REPRESSION/

NGG1p/ADA3p is a yeast dual function regulator required for the comple te glucose repression of GAL4p-activated genes (Brandl, C. J., Furlane tto, A. M., Martens, J. A., and Hamilton, K. S. (1993) EMBO J. 12, 525 5-5265). Evidence for a direct role for NGG1p in regulating activator function is supported by the finding that NGG1p is also required for t ranscriptional activation by GAL4p-VP16 and LexA-GCN4p (Pina, B., Berg er, S. L., Marcus, G. A., Silverman, N., Agapite, J., and Guarente, L. (1993) Mol. Cell. Biol. 13, 5981-5989). By analyzing deletion derivat ives of the 702-amino acid protein, we identified a region essential f or glucose repression within residues 274-373. Essential sequences wer e further localized to a segment rich in Phe residues that is predicte d to be an amphipathic alpha helix. As well as finding mutations withi n this region that reduced glucose repression, we identified mutations that made NGG1p a better repressor. In addition, NGG1p probably repre sses GAL4p activity as part of a complex containing ADA2p because sing le and double disruptions of ngg1 and ada2 had comparable effects on g lucose repression. We also localized a transcriptional activation doma in within the amino-terminal amino acids of NGG1p that is proximal or overlapping the region required for glucose repression. Activation by GAL4p-NGG1p(1-373) requires ADA2p; however, activation by GAL4p-NGG1p( 1-308) is ADA2p-independent. This suggests that a site required for AD A2p interaction lies between amino acids 308 and 373 and that ADA2p ha s a regulatory role in activation by GAL4p-NGG1p(1-373).