Why restriction enzymes cut (usually) at palindromic sequences?

Question

Restriction enzymes usually cut only at palindromic sequences. Is there any specific reason for that ? Is there any advantage for bacteria if it cuts up virus at this type of sequences ?

Answer 1

Type II restriction enzymes cut at palindromic sequences because the enzyme is a homodimer, with two active sites to cleave DNA in each strand. Because the homodimer is made of identical proteins they have identical recognition specificity meaning the sequence in each strand much be the same and therefore form a palindrome.