Which enzyme is responsible for cutting DNA at specific locations, enabling the construction of recombinant DNA?

Restriction enzymes

The correct answer is Option (3) -  Restriction enzymes

Restriction enzymes are responsible for cutting DNA at specific locations. They are molecular scissors that recognize specific DNA sequences and cleave the DNA at those sites. This property of restriction enzymes allows scientists to isolate specific DNA fragments and use them in the construction of recombinant DNA molecules.

In 1963, two enzymes responsible for restricting the growth of bacteriophage in Escherichia coli were isolated. One enzyme added methyl groups to DNA, while the other enzyme cut DNA. The enzyme that cut DNA was called restriction endonuclease.

The first restriction endonuclease, Hind II, was isolated and characterized five years later. Hind II was found to always cut DNA molecules at a particular point by recognizing a specific sequence of six base pairs. This specific base sequence is known as the recognition sequence for Hind II.

Today, there are more than 900 restriction enzymes that have been isolated from over 230 strains of bacteria, each of which recognizes different recognition sequences.