Question

What happens if a DNA molecule is treated by first Exonuclease III and then followed by treatment with S1 nuclease?

(a) The molecule is shortened only from 3’ end

(b) The molecule is shortened only from 5’ end

(c) The molecule is shortened from both the ends

(d) Only Exonuclease acts and S1 doesn’t acts

The question was posed to me in an interview.

My enquiry is from Exonucleases in division Basics of Genetic Engineering of Genetic Engineering

Answer 1

The correct answer is (c) The molecule is shortened from both the ends

For explanation: The molecule is shortened from both the ends. It is so because as firstly Exonuclease III acts, single stranded ends are produced on both the sides. These are further acted upon by S1 nuclease and thus the molecule is shortened from both the sides.