HMGB1 MOBILITY DEPENDS ON THE PROTEIN C-TAIL AND THE POSTSYNTHETIC ACETYLATION

High-mobility group box 1 protein (HMGB1) is a highly conserved nuclear protein, that facilitates DNA bending, stabilizes nucleosome formation, and modulates the interactions of regulatory molecules with their targets. HMGB1 is involved in practically all chromatin dependent cellular processes. These properties of HMGB1 were shown to be modulated by the acidic C-terminal domain of the molecule as well as by some post-synthetic modifications such as acetylation. As HMGB1 shows low if any sequence specificity we hypothesized that protein mobility in the nucleus is an important feature for its complex functions. We used Fluorescent Recovery After Photobleaching (FRAP) to determine the protein mobility and to examine if there is any difference in the mobility of its modified forms. Our experiments showed that the truncated protein has significantly lower rate of mobility compared to the full length HMGB1; interestingly the mobility of the truncated form was even further decreased when mutation in the site for acetylation was introduced. FRAP analysis revealed that HMGB1 is an extremely mobile protein which probably scans rapidly the whole chromatin matrix to find the places and the processes where it is needed. As the velocity of the protein decreases when the sites for post-synthetic acetylation are mutated we presume that acetylation takes an important place in the tuning of the mobility of HMGB1.