Mutation question

Question

A mutant yeast strain is found with a mutation affecting a tRNATyr. The wild type normally produces a tRNA that recognizes the codon 5’-UAC-3’, and is charged with the amino acid Tyrosine (Tyr) – tRNATyr. The mutant’s tRNA is still charged with Tyr, but the anticodon is mutated and now has the sequence 5’-UUA-3’. What effect will this have on translation in these yeast cells? How will the proteins produced be different?

Answer 1

When the tRNA anticodon is mutated to \(5'-UUA-3'\), it will recognize the complementary mRNA codon \(5'-UAA-3'\). Because \(5'-UAA-3'\) is a nonsense (stop) codon, this mutation creates a nonsense suppressor tRNA.

During translation, the mutant tRNA will bind to the \(UAA\) stop codon and insert Tyrosine into the growing polypeptide chain instead of terminating translation.

This means that the mutant could produce a new protein at this codon. It could be beneficial or negative to the mutant strain, depending on the codon's base function. If the base function is quiet, new beneficial (evolution) or negative protein (devolution) could be replicated. Assuming the base function of the codon is wild type and healthy, the new protein could be detrimental (devolution) or allow an altered metabolism to its environment (evolution.)