HMG box A in HMG2 protein functions as a mediator of DNA structural alteration together with box B.

Nonhistone protein HMG2, like HMG1, binds with B-DNA in a sequence-nonspecific manner and causes structural alterations in DNA such as bending, kinking and unwinding. Here, we studied the functions of HMG2 domains in the DNA structural alteration and modulation by using various HMG2 peptides, and we demonstrated several new findings. The HMG box itself as a DNA-binding motif may have the basic function of inducing curvature, resulting in the apparent DNA bending in the DNA cyclization assay, but not of abruptly kinking DNA. The DNA-binding activity of HMG box B, which is enhanced by the presence of box A, together with the flanking regions of box B, causes DNA bending accompanying the kinking of the DNA main chain. The DNA unwinding accompanied by DNA kinking diminishes cruciform structures in supercoiled DNA. Analysis using mutant peptides for box A confirmed that box A in HMG2 functions as a mediator of DNA structural alteration together with box B. The present studies on the functional properties of the respective regions of HMG2 may help to elucidate the protein function.