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. 2014 Feb 4;9(2):e88097. doi: 10.1371/journal.pone.0088097

Figure 1. Model of transcription attenuation of the B. subtilis trp operon.

Figure 1

Bold black letters designate the complementary strands of the attenuator (C/D) (highlighted in blue) and antiterminator (A/B) RNA structures. TRAP is shown in a ribbon diagram with each subunit in a different color. The 11 (G/U)AG repeats of the TRAP binding site are circled and numbered in green. Small black numbers indicate RNA residues relative to the start of transcription. When tryptophan is limiting, the AB antiterminator RNA structure forms, allowing read through of the trp operon. In excess tryptophan, TRAP binds to the nascent RNA and prevents formation of the antiterminator structure, which allows formation of the attenuator, leading to transcription termination.