You expect that a mutation in E.coli that was recently isolated results in loss of enzyme R activity.In looking for the gene,you find comparable sequences.Using an in vitro transcription translation system,you use the gene obtained from the mutant,as well as a wild type E.coli as a control.Following protein isolation and gel electrophoresis,you observe that the wild type E.coli produces a protein that is 35K in size,corresponding to enzyme R.However,the mutant strain produces a protein that is 25K in size.What does this information suggest?
A)A nonsense mutation has occurred, resulting in a truncated, nonfunctional product in the mutant.
B)A large addition has occurred in the wild type strain, such that approximately 35 tandem repeats of this gene are present and are biologically active.
C)A missense mutation has occurred, resulting in a truncated, nonfunctional product in the mutant.
D)all of the above
E)Not enough information is given.

Question

Quizplus · Accepted Answer

The smaller size of the protein produced by the mutant strain suggests that a nonsense mutation has occurred, causing a premature stop codon that results in a truncated, nonfunctional product. This is supported by the fact that the mutant strain is unable to produce functional enzyme R. Choice B is unlikely because it suggests the wild type strain has a large addition that is not present in the mutant strain. Choice C is also unlikely because a missense mutation typically results in a different amino acid sequence, but the same size protein as the wild type. Therefore, the best choice is A.

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