Which of the following statements regarding attenuation of the trp operon is NOT true?
◦ It is controlled by alternative folding of the mRNA synthesized from the trpL region.
◦ Translation of a trpL coding sequence into a 14-amino acid polypeptide (including the methionine of the start codon and two back-to-back tryptophan codons) is crucial to its function.
◦ If the two tryptophan codons were changed to arginine codons the operon would no longer be sensitive to tryptophan levels but would instead be sensitive to arginine levels.
◦ When tryptophan levels are low, the ribosome will occupy regions 1 and 2 after completing translation of the coding sequence, regions 3 and 4 will pair, and transcription will terminate.
◦ When tryptophan levels are high, the formation of a 3-4 stem loop followed by the poly-U string will prevent expression of the structural genes of the operon.
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The attenuation model regulating the tryptophan operon