Acidic C-tail of HMGB1 is required for its target binding to nucleosome linker DNA and transcription stimulation

HMGB 1, a nonhistone chromosomal protein in higher eukaryotic nuclei, consists of two DNA binding motifs called HMG boxes and an acidic C-tail comprising a continuous array of 30 acidic amino acid residues. In the preceding study, we showed that the acidic C-tail of HMGB I is required for transcription stimulation accompanied by chromatin decondensation in cultured cells. However, details of the involvement of the acidic C-tail in transcription stimulation were not clear. To clarify the mechanism of transcription stimulation by the acidic C-tail, we assessed the effect of the acidic C-tail on the transcription stimulation and nucleosome binding. Transcription stimulation assays using acidic C-tail deletion mutants showed that the five amino acid residues at the C-terminal end of HMGB 1, a DDDDE sequence, are essential for the stimulation. The DDDDE sequence was also required for the preferential binding of HMGB I to nucleosome linker DNA, which is a cognate HMGB 1 binding site in chromatin. Cross-linking and far-Western experiments demonstrated that the DDDDE sequence interacts with the core histone H3 N-tail. These results strongly suggest that the interaction between the DDDDE sequence of HMGB I and the H3 N-tail is a key factor for the transcription stimulation by HMGB I as well as the preferential binding of HMGB I to chromatin.