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. Author manuscript; available in PMC: 2010 Apr 15.
Published in final edited form as: Curr Opin Chem Biol. 2008 Sep 9;12(6):640–646. doi: 10.1016/j.cbpa.2008.08.011

Figure 4.

Figure 4

Effect of co-transcriptional folding/unfolding of the histidine (his) terminator hairpin upon transcription. Adapted from [55••]. (a) Force is applied to an RNA transcript during transcription, biasing the structure (folded/unfolded) of the terminator hairpin as the motion of polymerase is continuously measured. (b) Efficiency of transcription is found to depend on force through two mechanisms that work in conjunction: (i) shearing of the RNA/DNA hybrid at a U-rich tract (yellow), most evident at high force, and (ii) folding/unfolding of the intrinsic terminator hairpin (black), most evident at low force. (c) Model of the energy landscape for termination, where the terminator hairpin lowers the barrier to termination. Force applied to the RNA can raise this barrier in the presence of the hairpin by causing the hairpin to unfold (dashed black line), but can lower the barrier in the absence of the hairpin by shearing the RNA/DNA hybrid at the U-tract (dashed yellow line).