G21. Several biosynthetic operons in bacteria are regulated by attenuation: enzymes needed to synthesize an amino acid s

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G21. Several biosynthetic operons in bacteria areregulated by attenuation: enzymes needed to synthesize an aminoacid such as tryptophan are made only if that amino acid is notpresent. Attenuation depends on all of the following features ofgene expression except one. Which is the exception?
A) simultaneous transcription and translation of amessage
B) transcript termination by a stem-loop structure inRNA
C) stalling of ribosomes in the absence of a neededamino acid
D) a short leader peptide encoded at the start of apolycistronic transcript
E) binding of a repressor protein to anoperator.
THE CORRECT ANSWER IS E.
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