Which is the first restriction endonuclease discovered?

Which of the following is not used for isolation of $\text{DNA}$ from cells?

$A$ - Restriction endonucleases are also called 'molecular scissors'.
$R$ - When fragments generated by restriction endonucleases are mixed,they join together due to their sticky ends.

An enzyme catalysing the removal of nucleotides from the ends of $DNA$ is:

Which bacterium is commonly used in genetic engineering?

Identify the palindromic nucleotide sequence.