ADA5 SPT20 LINKS THE ADA AND SPT GENES, WHICH ARE INVOLVED IN YEAST TRANSCRIPTION/

In this report we describe the cloning and characterization of ADAS, a gene identified by resistance to GAL4-VP16-mediated toxicity. ADAS bi nds directly td the VP16 activation domain but not to a transcriptiona lly defective VP16 double point mutant. Double mutants with mutations in ada5 and other genes (ada2 or ada3) isolated by resistance to GAL4- VP16 grow like ada5 single mutants, suggesting that ADAS: is in the sa me pathway as the other ADA genes. Further, ADA5 cofractionates and co precipitates with ADA3. However, an ada5 deletion mutant exhibits a br oader spectrum of phenotypes than mutants with null mutations in the o ther ADA genes. Most interestingly, ADAS is identical to SPT20 (S. M. Roberts and F. Winston, Mel. Cell. Biol. 16:3206-3213, 1996), showing that it shares phenotypes with the ADA and SPT family of genes. Of the other SPT genes tested, mutants with mutations in SPT7 and, strikingl y, SPT15 (encoding the TATA-dinding protein) show resistance to GAL4-V P16. We present a speculative pathway pf transcriptional activation in volving the ADA2-ADA3-GCN5-ADA5 complex and the TATA-binding protein.