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 foun d in many proteins that bind preferentially to DNA of irregular struct ures in a sequence-independent manner and can bend the DNA, We show he re that GST-fusion proteins of HMG domains from HMG1 and HMG2 promote a triple-stranded complex formation between DNA containing the (GGA/TC C)(11) repeat and oligonucleotides of d(GGA)(11) probably due to G:G b ase pairing, The activity is to reduce association time and requiremen ts 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 fr om HMG1/2 but is common to those from other members of the HMG-box fam ily of proteins, Interestingly, the box-AB and box-B of HMG1 bend DNA containing the repeat, but SRY fails to bend in a circularization assa y, The difference suggests that the two activities of association-prom otion 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 ch romatin.