There are enzymes called aminoacyl-tRNA synthetases that attach tRNAs to the appropriate amino acid. Assume that the aminoacyl-tRNA synthetase that attaches tryptophan to its tRNA in an E. coli mutant strain is only partially active. It is active enough for the strain that carries it to be viable but is much less active than that of wild-type cells. What would be the expected effect of this mutation on attenuation in the trp operon?
A) Pairing of regions 3 and 4 in the 5' UTR of the RNA will be enhanced so attenuation will increase in the presence of tryptophan.
B) Pairing of regions 2 and 3 in the 5' UTR of the RNA will be decreased so attenuation will increase in the presence of tryptophan.
C) Pairing of regions 3 and 4 in the 5' UTR of the RNA will be decreased so attenuation will decrease in the presence of tryptophan.
D) Attenuation will not change but the trp repressor will be more active and the transcription of the trp operon structural genes will be decreased in the presence of tryptophan.
E) Attenuation will be decreased in the absence of tryptophan but will be enhanced in the presence of tryptophan.

Question

Quizplus · Accepted Answer

A partially active aminoacyl-tRNA synthetase for tryptophan would lead to less charged tRNA^Trp, causing ribosomes to stall at the trp codons in the leader peptide. This stalling allows regions 2 and 3 to pair, preventing regions 3 and 4 from forming the attenuator structure, thus decreasing attenuation in the presence of tryptophan.

There Are Enzymes Called Aminoacyl-TRNA Synthetases That Attach TRNAs to the Appropriate