A poison added to an in vitro translation mixture containing mRNA molecules with the sequence 5?-AUGAAAAAAAAAAAAUAA-3? has the following effect:
the only product made is a Met-Lys dipeptide that remains attached to the ribosome. What is the most likely way in which the poison acts to inhibit protein synthesis?
(a) It inhibits peptidyl transferase activity.
(b) It inhibits movement of the small subunit relative to the large subunit.
(c) It inhibits release factor.
(d) It mimics release factor.
Choice (b) is correct. Choice (a) would prevent all peptide bond formation. Choice (c) would have no effect on translation until the stop codon was reached. Choice (d) would be likely to result in a mixture of polypeptides of various lengths; a poison mimicking a release factor could conceivably cause only Met-Lys to be made, but this dipeptide would not remain bound to the ribosome.
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