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. Author manuscript; available in PMC: 2013 Apr 6.
Published in final edited form as: Wiley Interdiscip Rev RNA. 2011 Jan 12;2(2):299–311. doi: 10.1002/wrna.63

Figure 2.

Figure 2

Alternative secondary structures of a riboswitch that regulates transcription. The "off" state (left) is characterized by SAM bound to the aptamer domain (cyan box) which incorporates a sequence that is shared with the downstream expression platform (marked as "1"). This forces the expression platform (yellow box) to form a terminator stem-loop. In the "on" state (right) the lack of SAM binding allows the expression platform to form an antiterminator element using the sequence shared between the two domains. Note the mutual exclusivity of formation of the antiterminator and terminator through differential partitioning of sequences "1" and "2".