Question

Choose the incorrect statement in respect to topoisomerase I.

(a) It is used to cleave only one DNA strand

(b) It leaves at the recognition sequence –C/TCCTT- and is covalently attached to one end of the cleaved molecule

(c) The supercoiling of the DNA strand is altered and then it is sealed again by the enzyme

(d) It is slower than the normal DNA ligase

The question was asked at a job interview.

Enquiry is from Modifications in Cloning Methods, Linkers,  Adaptors and Cassettes in division Simple Cloning of Genetic Engineering

Answer 1

Right answer is (d) It is slower than the normal DNA ligase

Easiest explanation: Topoisomerase I is an enzyme used for cleaving of one DNA strand. It leaves at the recognition sequence –C/TCCTT- and is covalently attached to one end of the cleaved molecule. The supercoiling of the DNA strand is altered and then it sealed by the enzyme again. It is usually faster than DNA ligase. Topoisomerase II is used for cleaving both the strands.