YTAF(II)61 HAS A GENERAL ROLE IN RNA-POLYMERASE-II TRANSCRIPTION AND IS REQUIRED BY GCN4P TO RECRUIT THE SAGA COACTIVATOR COMPLEX

We obtained a recessive insertion mutation in the gene encoding yeast TBP-associated factor yTAF(II)61/68 that impairs Gcn4p-independent and Gcn4p-activated HIS3 transcription. This mutation also reduces transc ription of seven other class II genes, thus indicating a broad role fo r this yTAF(II) in RNA polymerase II transcription. The Gcn4p activati on domain interacts with multiple components of the SAGA complex in ce ll extracts, including the yTAF(II) proteins associated with SAGA, but not with two yTAF(II)s restricted to TFIID. The taf61-1 mutation impa irs binding of Gcn4p to SAGA/yTAF(II) subunits but not to components o f holoenzyme mediator. Our results provide strong evidence that recrui tment of SAGA, in addition to holoenzyme, is crucial for activation by Gcn4p in vivo and that yTAF(II)61 plays a key role in this process.