These extract contain the first known restriction endonucleases, enzymes that attack and digest bacteriophage DNA but not their own. K-12 and B were found to have chemically modified bases which were methylated . Additional studies with other strains indicate that different strains had specific methylated bases. Restriction endonucleases are commonly named after the bacterium from which it was isolated. Leaves 5' overhang.
Middle base can be either cytosine or guanine.
Leaves 5' overhang. Different recognition sites may have non-complementary sequences. Leaves 5' overhang. Leaves 3' overhang. Leaves 5' overhang.