| Co immunoprecipitation experiments showed that TFIIS can bind the Cdk 8 module and SAGA in cell free extracts . spt8Delta and dst1Delta mutants were sensitive to nucleotide depleting drugs and epistatic to null mutants of the RNA polymerase 2 subunit Rpb 9 , suggesting that their elongation defects are mediated by Rpb 9 . rpb9Delta , spt8Delta and dst1Delta were lethal in cells lacking the Rpb 4 subunit . ^^^ It is proposed that TFIIS and the Spt 8 containing form of SAGA co operate to rescue RNA polymerase 2 from unproductive elongation complexes , and that the Cdk 8 module temporarily blocks transcription during transcript cleavage . . ^^^ |