ASSOCIATION OF THE HISTONE-LIKE PROTEIN HBSU WITH THE NUCLEOID OF BACILLUS-SUBTILIS

To investigate the physiological role of the essential histone-like pr otein of Bacillus subtilis (HBsu) in the nucleoid structure, a fusion to the green fluorescent protein (GFP) of Aequorea victoria was constr ucted. This purified fusion protein, HBsuGFP, showed a threefold-reduc ed affinity to DNA compared to unmodified HBsu; however, in gel mobili ty shift experiments HBsuGFP DNA-binding was greatly enhanced in the p resence of low HBsu concentrations. Additional production of HBsu also had a positive effect on the retarded growth of a B. subtilis strain, PK9C8, which expresses only hbs-gfp (encoding HBsuGFP). HBsu seemed t o influence not only growth but also nucleoid structure, as monitored by DNA staining and fluorescence microscopy. Without HBsu production, strain PK9C8 showed a relaxed nucleoid structure associated with HBsuG FP, However, a highly compact nucleoid structure that coincides with t he fluorescence of the fusion protein was visualized when HBsu synthes is was induced. This provides the first evidence for in vivo associati on of HBsu in DNA packaging and its consequence on cell growth.