A novel activity of HMG domains: Promotion of the triple-stranded complex formation between DNA containing (GGA/TCC)(11) and d(GGA)(11) oligonucleotides

The high mobility group protein (HMG)-box is a DNA-binding domain found in many proteins that bind preferentially to DNA of irregular structures in a sequence-independent manner and can bend the DNA, We show here that GST-fusion proteins of HMG domains from HMG1 and HMG2 promote a triple-stranded complex formation between DNA containing the (GGA/TCC)(11) repeat and oligonucleotides of d(GGA)(11) probably due to G:G base pairing, The activity is to reduce association time and requirements of Mg2+ and oligonucleotide concentrations, The HMG box of SRY, the protein determining male-sex differentiation, also has the activity, suggesting that it is not restricted to the HMG-box domains derived from HMG1/2 but is common to those from other members of the HMG-box family of proteins, Interestingly, the box-AB and box-B of HMG1 bend DNA containing the repeat, but SRY fails to bend in a circularization assay, The difference suggests that the two activities of association-promotion and DNA bending are distinct, These results suggest that the HMG-box domain has a novel activity of promoting the association between GGA repeats which might be involved in higher-order architecture of chromatin.