High glutamic and aspartic region in nonhistone protein HMG(1+2) unwinds DNA double helical structure

A high mobility group (HMG) nonhistone protein fraction HMG(1+2) from pig thymus, composed of HMG1 and HMG2, has an activity to unwind the double helical structure of DNA (Yoshida, M. and Shimura, K. (1984) J. Biochem. 95, 117-124; Makiguchi, K., Chida, Y., Yoshida, M., and Shimura, K. (1984) J. Biochem. 95, 423-429). The HMG(1+2) was cleaved with trypsin, followed by peptide separation by ionic exchange column chromatography with Polybuffer exchanger PBE94. The effects of five peptide fractions thus obtained on the thermal denaturation of DNA were measured. A peptide containing a high glutamic and aspartic (HGA) region, of the composition Glu34Asp15Lys3, unwound DNA depending on the presence of Mg2+ or Ca2+, while other peptide fractions did not, suggesting that the HGA region in HMG(1+2) is an active site in the unwinding reaction of the double helical structure of DNA.