NGG1p/ADA3p and ADA2p are dual function regulators that stimulate or inhibit a set of yeast transcriptional activator proteins. In vitro, NGG1p and ADA2p associate in a complex that also contains GCN5p (Horiuchi, J., Silverman, N., Marcus, G. A., and Guarente, L. (1995) Mol. Cell. Biol. 15, 1203-1209). We have found that NGG1p and ADA2p are coimmunoprecipitated from yeast whole cell extracts. In fact, <2% of cellular ADA2p was not associated with NGG1p. Also in agreement with their association in vivo, the stability of ADA2p and NGG1p depended on the presence of each other. In addition, three NGG1p-and ADA2p-containing peak fractions were resolved by Q-Sepharose Fast Flow ion-exchange chromatography of whole cell extract. The presence of another high molecular mass complex was supported by the separation of one of the NGG1p-and ADA2p-containing peak fractions by gel-filtration chromatography. Together, the combination of ion-exchange and gel-filtration chromatography suggests a total of four complexes, two with sizes of >2 MDa and single complexes of ϳ900 and 200 kDa. At least one of these complexes was found to associate with the TATA-binding protein (TBP) since TBP was present in immunoprecipitates with NGG1p. The association of TBP with the ADA proteins required amino acids 274 -307 of NGG1p, a region of NGG1p required for activity. This supports a role for NGG1p in the interaction with TBP and suggests that the interaction with TBP is functionally relevant.Activated transcription by RNA polymerase II requires the action of the basal transcriptional machinery, sequence-specific activator proteins, and coactivator or mediator proteins (1). Coactivators positively influence activator function either by providing a regulatory interface between the basal machinery and the activator protein or by enabling these components to contend with a DNA template in the form of chromatin. Coactivators have generally been found as components of regulatory complexes. The TBP 1 ⅐TBP-associated factor complex, the RNA polymerase II holoenzyme complex, and the Swi⅐Snf complex represent principal examples (reviewed in Refs. 2-4). The mechanisms and component structure of these complexes may overlap as suggested by the finding of Swi/Snf components (5) within the RNA polymerase II holoenzyme (6), the TBP-associated factor complex, and transcription factor IIF (7).Probably through related mechanisms, coactivator complexes can also be involved in repression. We initially discovered NGG1 based on its requirement for full inhibition of the GAL4 activator protein in glucose media (8). NGG1p likely acts as a more general repressor because transcriptional activation by the carboxyl-terminal activation domain of PDR1p is enhanced in a ngg1 background (9). Guarente and co-workers (10) independently isolated NGG1/ADA3 based on suppression of the toxicity of overexpression of VP16 in yeast. Mutations within four ADA genes, ADA2, NGG1/ADA3, GCN5/ADA4, and ADA5, suppress the toxicity of VP16 by inhibiting its ability to activate transcription (...

The relationship of polyphosphoinositide metabolism to erythrocyte ATP levels was examined. Turnover of polyphosphoinositides was not closely dependent on ATP as it is reported to be in yeast. Neomycin increased 32P incorporation into diphosphoinositide and to a lesser extent into triphosphoinositide without affecting intracellular ATP. Treatment of intact cells with ionophore A23187 resulted in a decrease of at least 80% in polyphosphoinositide levels which followed a decrease in cellular ATP and an increase in phosphatidate. The results indicate that polyphosphoinositide turnover does not regulate energy charge in the erythrocyte. However some of the events which follow treatment of erythrocytes with metabolic inhibitors or calcium and ionophore may be related to the accompanying decrease in polyphosphoinositide levels.