What experiment demonstrated that the 5'-to-3' exonuclease activity of DNA polymerase I was essential for cell viability?
What will be an ideal response?
In E. coli, the DNA Pol I polAex1 mutant strain survives at 37?C but dies at 42?C. This was shown to be because the mutant DNA Pol I enzyme had normal activity at 37?C but a defective 5'-to-3' activity at 42?C. This demonstrated that the 5'-to-3' exonuclease activity of DNA Pol I was essential for cell survival.
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