Which one of the following is indispensable in genetic engineering?

$A$ specific recognition sequence identified by endonucleases to make cuts at specific positions within the $DNA$ is:

If foreign $DNA$ is inserted into $pBR322$ at the $Pst \, I$ site and this plasmid is introduced into bacteria,then:

Would you choose an exonuclease while producing a recombinant $DNA$ molecule?

In gel electrophoresis, the separated $DNA$ fragments can be visualized only after staining the $DNA$ with a compound known as ............. followed by exposure to $UV$ radiation.

$A$ : During gel electrophoresis,the $DNA$ fragments move towards the anode.
$R$ : $DNA$ fragments are negatively charged molecules.