Palindromes, hairpins, cruciforms, and mirror repeats in DNA. (a) A palindromic sequence in DNA, such as the recognition site for the EcoRI restriction enzyme, is the same when reading from 5′ to 3′ on either strand of the DNA. (b) Inverted repeats within a single strand of DNA can be converted into a hairpin, which is double-stranded in the stem region. Inverted repeats within a double-stranded DNA sequence can form a cruciform (double-hairpin) structure. (c) DNA can also contain mirror repeats, such as TTAGCACCACGATT, which are not palindromic.