The eukaryotic transcript elongation factor TFIIS enables RNA polymerase II to read through blocks to elongation in vitro and interacts genetically with a variety of components of the transcription machinery in vivo. In Saccharomyces cerevisiae, the gene encoding TFIIS (PPR2) is not essential, and disruption strains exhibit only mild phenotypes and an increased sensitivity to 6-azauracil, The nonessential nature of TFIIS encouraged the use of a synthetic lethal screen to elucidate the in vivo roles of TFIIS as well as pro,ide more information on other factors involved in the regulation of transcript elongation. Several genes were identified that are necessary for either cell survival or robust growth when the gene encoding TFIIS has been disrupted. These include UBP3, KEX2, STT4, and SI SWI2/SNF2. SWII and SNF5 disruptions were also synthetically lethal with ppr Delta suggesting that the reduced ability to remodel chromatin confers the synthetic phenotype. The synthetic phenotypes show marked osmosensitivity and cytoskeletal defects, including a terminal hyperelongated bud phenotype with the Swi-Snf complex. These results suggest that genes important in osmoregulation, cell membrane synthesis and integrity, and cell division mag require the Swi-Snf complex and TFIIS for efficient transcription, The detection of these genetic interactions provides another functional link between the Swi-Snf complex and the elongation machinery.
