The thermostability of DNA-binding protein HU from bacilli

The primary and tertiary structures of DNA-binding protein HUfrom Bacillus stearothermophilus are already known. The primarystructure has been previously determined for HU from the closelyrelated B.globigü and the determinations of the sequencesfrom B.caldolyticus and B.subtilis are described here. Thesebacteria have optimum growth temperatures of > 70C (B.caldolyticus),65C (B.stearothermophilus), 37C (B.subtilis) and 30C (B.globigü).in vitro measurements from circular dichroic spectra describedhere give T_m values reflecting these growth temperatures, of68, 64, 43 and 41C respectively. We discuss here the relativethermostability of the four proteins in terms of the amino aciddifferences between the sequences and the three-dimensionalmodel of the B.stearothermophilus HU. The current model forthe interaction of the protein with DNA is only discussed interms of its relevance with regard to thermostability.