HMGB1 is a multidomain protein that binds and bends DNA non-sequence specifically.
DNA bending by HMGB1 domains was monitored using single-molecule FRET.
FL HMGB1 bent DNA slightly more than the A box and B box individually.
Deleting the HMGB1 C-terminal tail caused DNA to be bent into a higher FRET state.
Data support the model that the C-terminal tail impedes DNA binding by the B box.