Artificial recruitment of TFIID, but not RNA polymerase II holoenzyme, activates transcription in mammalian cells

In yeast cells, transcriptional activation occurs when the RNA polymerase I I (Pol II) machinery is artificially recruited to a promoter by fusing indi vidual components of this machinery to a DNA-binding domain. Here, we show that artificial recruitment of components of the TFIID complex can activate transcription in mammalian cells. Surprisingly, artificial recruitment of TATA-binding protein (TBP) activates transiently transfected and chromosoma lly integrated promoters with equal efficiency, whereas artificial recruitm ent of TBP-associated factors activates only chromosomal reporters. In cont rast, artificial recruitment of various components of the mammalian Pol II holoenzyme does not confer transcriptional activation, nor does it result i n synergistic activation in combination with natural activation domains. In the one case examined in more detail, the Srb7 fusion failed to activate d espite being associated with the Pol II holoenzyme and being directly recru ited to the promoter. Interestingly, some acidic activation domains are les s effective when the promoter is chromosomally integrated rather than trans iently transfected, whereas the Spl glutamine-rich activation domain is mor e effective on integrated reporters. Thus, yeast and mammalian cells differ with respect to transcriptional activation by artificial recruitment of th e Pol II holoenzyme.