The stabilized structural array of two HMG1/2-boxes endowed by a linker sequence between them is requisite for the effective binding of HMG1 with DNA

High mobility group (HMG) protein 1 contains two DNA binding motifs, called HMG1/2-boxes, linked with a linker region. The functional relationships between the two boxes and the mechanism of involvement of the linker region for effective binding of HMG1 were examined. The binding analyses of truncated HMG1 peptides with DNA indicated that the structural array of two boxes stabilizes the interaction of HMG1 with DNA. The mutation analyses of the linker region suggested that the region is equipped with tolerance for the deletion of a few amino acid residues to allow appropriate binding of the two boxes with DNA, and that the basic cluster in the linker sequence is in a position to interact with DNA. The existence of tolerance for the linker sequence was found to be conserved during the evolution of HMG1 protein homologues. A structural model for array of two boxes associating with DNA minor groove was constructed on the basis of the experimental results and energy minimization. The model proposes that the DNA binding region in HMG1 covers an 18 bp DNA region and induces its bending by about 140 degrees. The linker region may function to maintain the structural array of two HMG1/2-boxes by direct interaction with DNA.