A researcher using a model eukaryotic experimental system has identified a tempe

Question

A researcher using a model eukaryotic experimental system has identified a temperature- sensitive mutation RNA polymerase II. This mutation is a missense mutation. Mutants have a recessive lethal phenotype at the higher restrictive temperature but grow normally at a lower, permissive temperature. To identify the genes whose products interact with the subunit of RNA polymerase 2, the researcher designs a screen to isolate mutation will act as suppressors of the temperature sensitive mutation.

**Do you expect the frequency of suppressor mutations to be similar to, much greater than, or much less than the frequency of new mutations at a typical eukaryotic gene? Explain.

Explanation / Answer

Missense mutations occur due to replacement of one nucleotide by another in a triplet codon which results in recognizing a different amino acid than the normal amino acid. This leads to the synthesis of a mutant protein.

Suppressor mutations are other secondary mutations following the missense mutation which had occurred. They can reverse the missense mutation and lead to production of normal protein. Suppressor mutations can be intergenic or intragenic.

Intergenic suppressor mutation (mutation in any gene in the genome) might not significantly reverse the production of mutant protein whereas intergenic suppressor mutation (mutation in same gene and site where the mutation had occurred) can revert to the production of normal protein instead of mutant protein.

Considering the huge genomic size of eukaryotic cell the frequency of occurrence of intergenic suppressor mutation exactly at the site of missense mutation is very low. Since the ability to restore missense mutation by most of the mutagen induced suppressor mutations are very exceptional.

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