Conformational studies of two non-histone chromosomal proteins and their interactions with DNA.

The conformational properties of two non-histone chromosomal proteins (high-mobility-group proteins 1 and 2) have been studied by spectroscopic methods. The interaction of high-mobility-group protein 1 with DNA has also been studied. 1. Circular dichroism results indicate that in the presence of salt both proteins are 40-50% helical between pH 1 and 9. Above pH 9 denaturation takes place. In the absence of salt the proteins denature below pH 4. 2. Nuclear magnetic resonance spectra show the presence of ring-current shifted peaks and perturbed aromatic resonances, demonstrating that the helix formation is accompanied by specific tertiary folding. 3. Nuclear magnetic resonance spectra of compelxes between high mobility group protein 1 and DNA demonstrate that a low ionic strength a portion of the molecule rich in lysine and containing all the aromatic residues is bound to DNA, whilst a more acidic region of the chain remains free from the DNA.