Properties of DNA-binding of HU heterotypic and homotypic dimers from Escherichia coli.

The interactions of three forms of HU dimer from Escherichia coli with DNA were compared. The complexes formed between HU and short DNA fragments (35 to 132 bp), uncurved oligodeoxyribonucleotide (oligo) with and without 5-bp deoxyriboadenosine (dA) stretches and curved oligo with 5-bp dA stretches, were analyzed by the gel retardation technique. The binding of HU homodimers to the DNA was less efficient than that of HU heterodimer, and the HU-1 homodimer had lower DNA-binding capacity than the HU-2 homodimer. The equilibrium dissociation constant (KD) for DNA of the HU-1 homodimer was 3 times that of the HU heterodimer. The HU dimers had two- to fourfold higher affinity for DNA duplexes containing 5-bp dA stretches, particularly for curved DNA. The binding of HU heterodimer to the DNA was inhibited more by the curved DNA competitor than the uncurved DNA competitor without dA stretches.