Figure 2, Operator DNA Sequences. 2a, above. The DNA sequence of each 17 base pair operator sequence in a genetic switch region of bacteriophage lambda. The operators (OR1, OR2, and OR3) each comprise palindromic sequences, found in left and right half-sites centered on a 2-fold symmetry axis. The middle of the palindromes lie ~10 base pairs (~34 angstroms apart. This spacing of partial palindromes provides the monomers of a dimeric cro or repressor protein nearly identical binding sites in each operator, separated by one complete turn of B-DNA.

2b. The DNA sequence (14 bp) of OR1-OR3 in a genetic switch region of bacteriophage 434, a relative of lambda. Note the perfect palindromes separated by ~10 bp (34 angstroms), as for lambda operators.