The EcoRI restriction enzyme--the first restriction enzyme isolated from E. Coli bacteria--is able to recognize the base sequence 5' GAATTC 3'. Restriction enzymes cut each strand of DNA between the G and the A in this sequence. This leaves "sticky ends" or single stranded overhangs of DNA. Each single stranded overhang has the sequence 5" AATT 3'. These overhanging ends will bond to a fragment of DNA which has the complementary sequence of bases.