Thermodynamic studies on synthetic lac operator core

The nine base pairs long central region of the $\text{lac}$ operator gene forms a stable double helix. A comparison of melting temperatures with other biologically useful oligonucleotides indicates the importance of specific base sequence. Binding constants measured with ethidium bromide (1.7 × 10⁵ M^?1), tyrosine (4.0 × 10³ M^?1), and glutamine (1.5 × 10³ M^?1), are interpreted in terms of the involvement of a relatively small number of amino acids in the $\text{lac}$ operator-repressor interaction.