The first restriction endonuclease type $II$ $…A..$, was isolated by Smith, Wilcox and Kelley from $…B…$ bacterium. It was formed to cut $DNA$ molecules at a particular point by recognizing a specific sequence of six base pairs, known as the $ …C….$ Here $A, B$ and $C $can be

$A$ : $DNA$ ligase plays an important role in recombinant $DNA$ technology.

$R$ : The linking of antibiotic resistance gene with plasmid vector became possible by enzyme $DNA$ ligase.

Cutting of a piece of $DNA$ from a plasmid was done with the help of $…A…$ enzymes, popularly known as $…B….$ Here $\mathrm{A}$ and $\mathrm{B}$ can be

Give differences : Restriction Endonuclease and Restriction Exonuclease

Assertion : Restriction enzymes cut the strand of $DNA$ to produce sticky ends.

Reason : Stickiness of the ends facilitates the action of the enzyme $DNA$ polymerase