In prokaryotes the restriction enzymes restricts the multiplication of foreign DNA e.g. bacteriophage DNA in bacteriurn. The restriction enzyme thus gives protection to the bacterium against the attack of bacteriophages. It is a defence mechanism of bacterial cells. There is present restriction modification system in prokaryotes the R.Es do not recognize and cut bacterial DNA by modification enzyme which add rnethyl group to the basis with in the sequence recognized by restriction enzymes. Bacteriophages do not infect eukaryotes. They have other defence mechanism.
