Bacteria and some other prokaryotes consists of restriction enzymes which are able to recognize specific sequences of DNA, called restriction sites. All restriction enzymes are able to recognize at least one or a few restriction sites. On identifying the target sequence, a restriction enzyme makes a double-stranded cut in the DNA molecule. This cut is a clear pattern which is easily identified as it is at or near the restriction site. A DNA fragment with complementary base fragments join with the DNA at the cut portion which is some times referred to as sticky ends
