HMG1 proteins from evolutionary distant organisms distort B-DNA conformation in similar way

The abundant high-mobility group proteins 1/2 (HMG1/2) represent a group of potent architectural elements of chromatin. They are able to induce strong bends and untwist DNA. Here, we compared the abilities of diverse HMG1 pro teins to distort the B-DNA conformation of 30-base pair DNA fragment. The D NA bending was measured in solution by monitoring fluorescence resonance en ergy transfer between fluorescence probes attached to opposite ends of the DNA fragment. Various insect and plant proteins which differ in size, in co mposition of their HMG1-box domains (HMG1-BD), and in composition of the N- and the C-terminally flanking regions were analyzed in these experiments. Despite these structural differences the extent of the induced changes in D NA conformation upon binding to various proteins was similar, as the estima ted bend angle was 150 +/- 20 degrees for all the tested proteins. Our resu lts suggest that a set of highly conserved residues stabilizing the tertiar y structure of the HMG1-BD mainly determines the extent of DNA bending in t he complex. Even extended positively charged regions flanking the HMG1-BD a re apparently not able to influence this conformational distortion of DNA. (C) 1999 Elsevier Science B.V. All rights reserved.