An Auxotrophic E - E Coli Strains That Have Both the Original Ade1^- Mutant

question 54

Essay

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 tRNA that has one base that is different from the wild-type tRNA. Explain how the lysine tRNA mutation allows synthesis of the normal ade1 enzyme.

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