Mutations from cordons specifying amino acid incorporation to one of the chain t

Question

Mutations from cordons specifying amino acid incorporation to one of the chain terminating (stop) cordons results in nonsense mutations that typically produce truncated proteins that are usually non-functional. It was discovered that some bacteria can protect themselves from nonsense mutations by having mutant tRNAs that can recognize a chain termination codon and insert an amino acid instead The result is a protein of normal length that may be functional. Propose a hypothesis to describe how bacteria with such mutant tRNA molecules still manage to correctly terminate their peptide chains successfully. How would you test your hypothesis? If an organism is found in an extreme environment with high temperatures would you expect it to have more AUG or GUG initiation codons? Why?

Explanation / Answer

a) Mutant tRNA compete with release factor for stop codons and supress the nonsense mutation in 10-40% cases while rest of time, release factor recognize the stop codon and terminate the polypeptide formation correctly.
b) The hypothesis can be tested using variable concentration of mutant tRNA and release factor to determine the effect of supressor mutantion in restoring the nonsense mutation and chain termination due to competition between mutant tRNA and release factor.

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