RNA polymerase II holoenzymes respond to transcriptional
activators and repressors that are regulated by signaling pathways. We
present evidence for a 'shortcut' mechanism in which the Snf1 protein
kinase of the glucose signaling pathway directly regulates
transcription by the yeast holoenzyme. First, in response to glucose
limitation, the Snf1 kinase stimulates transcription by holoenzyme
that has been artificially recruited to a reporter by a LexA fusion to
a holoenzyme component. Second, Snf1 interacts physically with
Srb/mediator proteins of the holoenzyme in both two-hybrid and
coimmunoprecipitation assays. Third, a catalytically hyperactive Snf1,
when bound to a promoter as a LexA fusion protein, activates
transcription in a glucose-regulated manner; moreover, this activation
is dependent on the integrity of the Srb/mediator complex. These
results suggest that direct regulatory interactions between signal
transduction pathways and RNA polymerase II holoenzyme provide a
mechanism for transcriptional control in response to important
signals.
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