How would you explain the mechanism of action of restriction enzymes?
Restriction enzymes recognize and cut at specific sequences.
Some recognize specific groups of 4 bases while many others recognize groups of 6. A 6-base restriction sequence may not exist even once in a given viral DNA molecule.
For example, the
recognition sequence of the E.coli RI enzyme is not present in the bacteriophage T7 DNA, which is 40,000 base pairs long.
Source for example: Recombinant DNA: A short course
by James D Watson, John Tooze and David T Kurtz
Scientific American Books