Use the Following to Answer Questions
an Auxotrophic E

Multiple Choice

Use the following to answer questions
An auxotrophic E. coli strain requires adenine to grow because of a mutation in a gene for an adenine synthesis enzyme. The following shows part of the wild-type and mutant alleles of the gene, including the start codon. The bottom strand is the template for transcription. $$\begin{array} { c c } \text { ade } 1 ^ { + } \text {wild-type allele } & \text { ade1 } ^ { - } \text {mutant allele } \\\text { 5'...TTATGGGCAAGATCCCA...3' } & \text { 5'....TTA TGGGCTAGATCCCA...3' } \\\text { 3'...AATACCCGTTCTAGGGT...5' } & \text { 3'...AATATGGGCTAGATCCCA...3' }\end{array}$$
-E. coli strains that have both the original ade1^- mutant allele shown above and a mutant allele for a gene that encodes a lysine tRNA are able to make some normal ade1 enzyme. The mutant lysine tRNA allele makes a tRNA that has one base that is different from the wild-type tRNA. Why might the mutant lysine tRNA allele affect overall cell growth?

A) The mutant tRNA^lysine will occasionally cause translation to continue beyond the normal stop codon on mRNAs that normally use UAG as a stop codon.
B) The premature stop codon from the ade1^- allele will always cause shortened proteins.
C) The mutant tRNA will prevent the translational machinery from recognizing the normal stop codon on the mRNA and so will result in incorrect proteins.
D) The mutant tRNA^lysine will recognize the stop codon on the mutant ade1^- allele and cause the protein to be terminated.
E) The mutant tRNA^lysine will incorporate a lysine at every UAG stop codon.