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. Author manuscript; available in PMC: 2015 Apr 28.
Published in final edited form as: Nat Commun. 2014 Oct 28;5:5270. doi: 10.1038/ncomms6270

Figure 6. Activation and counter-silencing are distinct mechanisms of transcription regulation.

Figure 6

Activation occurs predominantly at core ancestral promoters, as it requires a precisely positioned and oriented activator binding site (green arrow) relative to the TSS (bent arrow). In its “ON,” transcribed state, the promoter is bound by the activator, allowing a direct interaction with the RNAP (yellow) and an increase in transcription. Counter-silencing occurs at horizontally-acquired genes, where the counter-silencer protein (green ovals) binds in a variety of positions and orientations. A silencing protein (purple) represses transcription in the “OFF” state. In the transcribed “ON” state, the counter-silencer binds local DNA, disrupting the structure of the silencing complex and recruiting the RNAP holoenzyme, allowing transcription.