Abstract
H1.1 and H1.4 bind tightly to both short DNA oligomers and to CT-DNA (Ka≈1×107). Binding is accompanied by an unfavorable enthalpy change (∆H≈+22kcal/mol) and a favorable entropy change (−T∆S≈−30kcal/mol). The Tm for the H1.4/CT-DNA complex is increased by 9°C over the Tm for the free DNA. H1.4 titrations of the DNA oligomers yield stoichiometries (H1/DNA) of 0.64, 0.96, 1.29, and 2.04 for 24, 36, 48, and 72-bp DNA oligomers. The stoichiometries are consistent with a binding site size of 37±1bp. CT-DNA titration data are consistent with binding site sizes of 32bp for H1.1 and 36bp for H1.4. The heat capacity changes, ΔCp, for formation of the H1.1 and H1.4/CT-DNA complexes are −160calmol−1K−1 and −192calmol−1K−1 respectively. The large negative ΔCp values indicate the loss of water from the protein DNA interface in the complex.
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