Question

You have made a collection of mutant fruit flies that are defective in various aspects of DNA repair. You test each mutant for its hypersensitivity to three DNA-damaging agents: sunlight, nitrous acid (which causes deamination of cytosine), and formic acid (which causes depurination). The results are summarized in Table Q6-55, where a 'yes' indicates that the mutant is more sensitive than a normal fly, and blanks indicate normal sensitivity. Which mutant is most likely to be defective in the DNA repair polymerase?

Answer 1

To identify the mutant defective in DNA repair polymerase, look for increased sensitivity to DNA-damaging agents like sunlight (which forms pyrimidine dimers), nitrous acid (causing deamination), and formic acid (leading to depurination).

Step-by-step explanation:

The student has created a collection of mutant fruit flies with defects in various DNA repair mechanisms, and is attempting to identify which mutant is likely defective in the DNA repair polymerase. Considering that DNA repair polymerases are involved in the synthesis of DNA strands using an undamaged DNA strand as a template as well as correcting errors such as misincorporations or structural abnormalities in the DNA, the mutant that shows hypersensitivity to multiple DNA-damaging agents, including the sunlight-induced formation of pyrimidine dimers, deamination caused by nitrous acid, and depurination caused by formic acid, would suggest defects in the DNA repair polymerase.

Mutations in DNA polymerase can result in an increased number of errors during DNA replication, and since DNA polymerase has both a synthesis function and an exonuclease proofreading function, a defect in this enzyme would likely present sensitivity to several forms of DNA damage as seen in the aforementioned examples from sunlight, nitrous acid, and formic acid.