Recognition Sequences For Type II Endonucleases - The recognition sequences for Type II endonucleases form palindromes with rotational symmetry. In a palindrome, the base sequence in the second half of a DNA strand is the mirror image of the sequence in its first half; consequently, the complementary DNA strand of a double helix also shows the same situation.

But in a palindrome with rotational symmetry, the base sequence in the first half of one strand of a DNA double helix is the mirror image of the second half of its complementary strand. Thus in such palindromes, the base sequence in both the strands of a DNA duplex reads the same when read from the same end (either 5' or 3') of both the strands.