Nguyen Hong Ha, de la Tour Claire Bouthier, Toueille Magali, Vannier Françoise, Sommer Suzanne, Servant Pascale
Univ. Paris-Sud 11, CNRS UMR 8621, LRC CEA 42V, Institut de Génétique et Microbiologie, Bâtiment 409, Université Paris-Sud, F-91405 Orsay Cedex, France.
Mol Microbiol. 2009 Jul;73(2):240-52. doi: 10.1111/j.1365-2958.2009.06766.x. Epub 2009 Jun 28.
The nucleoid of radioresistant bacteria, including D. radiodurans, adopts a highly condensed structure that remains unaltered after exposure to high doses of irradiation. This structure may contribute to radioresistance by preventing the dispersion of DNA fragments generated by irradiation. In this report, we focused our study on the role of HU protein, a nucleoid-associated protein referred to as a histone-like protein, in the nucleoid compaction of D. radiodurans. We demonstrate, using a new system allowing conditional gene expression, that HU is essential for viability in D. radiodurans. Using a tagged HU protein and immunofluorescence microscopy, we show that HU protein localizes all over the nucleoid and that when HU is expressed from a thermosensitive plasmid, its progressive depletion at the non-permissive temperature generates decondensation of DNA before fractionation of the nucleoid into several entities and subsequent cell lysis. We also tested the effect of the absence of Dps, a protein also involved in nucleoid structure. In contrast to the drastic effect of HU depletion, no change in nucleoid morphology and cell viability was observed in dps mutants compared with the wild-type, reinforcing the major role of HU in nucleoid organization and DNA compaction in D. radiodurans.
包括耐辐射球菌在内的耐辐射细菌的类核采用高度浓缩的结构，在暴露于高剂量辐射后仍保持不变。这种结构可能通过防止辐射产生的DNA片段分散而有助于抗辐射。在本报告中，我们重点研究了HU蛋白（一种被称为类组蛋白的类核相关蛋白）在耐辐射球菌类核压缩中的作用。我们使用一种允许条件性基因表达的新系统证明，HU对于耐辐射球菌的生存能力至关重要。使用标记的HU蛋白和免疫荧光显微镜，我们表明HU蛋白遍布类核，并且当HU从热敏质粒表达时，其在非允许温度下的逐渐消耗会在类核分成几个实体并随后细胞裂解之前导致DNA解聚。我们还测试了缺乏Dps（一种也参与类核结构的蛋白）的影响。与HU缺失的剧烈影响相反，与野生型相比，在dps突变体中未观察到类核形态和细胞活力的变化，这加强了HU在耐辐射球菌类核组织和DNA压缩中的主要作用。
