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. 2005 Jun 24;1(1):e2. doi: 10.1371/journal.pcbi.0010002

Figure 1. The Leader-Transcript of the trp Operon in E. coli .

Figure 1

Attenuated transcription results in a 141-nucleotide (nt) transcript. Aborted transcription of the paused RNAP results in a 91-nt transcript. The transcript includes an open reading frame of 15 codons, encoding a very short-lived 14-residue leader peptide. The RNAP is released from the pause site when the seventh codon is read [17]. Two of the three codons in the control region (10 and 11) are trp codons. Also, ribosome stalling on the arg-codon (12) prevents I:II-hairpin formation and attenuation (see Figure 6). After reaching the stop codon, the ribosome dissociates in about 1 s. The II:III and III:IV conformations have similar stabilities, and the terminator is formed with 50% probability when the ribosome reaches the stop codon and dissociates from the transcript before region IV is available. This determines the basal read-through level of 10–15%.