iGenetics 3rd Edition by Peter Russell

Exercise 7

A researcher using a model eukaryotic experimental system has identified a temperature-sensitive mutation, rpIIA ts , in a gene that encodes a protein subunit of RNA polymerase II. This mutation is a missense mutation. Mutants have a recessive lethal phenotype at the higher, restrictive temperature, but grow at the lower, permissive (normal) temperature. To identify genes whose products interact with the subunit of RNA polymerase II, the researcher designs a screen to isolate mutations that will act as dominant suppressors of the temperature-sensitive recessive lethal mutation.
a. Explain how a new mutation in an interacting protein could suppress the lethality of the temperature-sensitive original mutation.
b. In addition to mutations in interacting proteins, what other type of suppressor mutations might be found?
c. Outline how the researcher might select for the new suppressor mutations.
d. 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?
e. How might this approach be used generally to identify genes whose products interact to control transcription?