Ogata Y, Inoue R, Mizushima T, Kano Y, Miki T, Sekimizu K
Department of Microbiology, Faculty of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
Biochim Biophys Acta. 1997 Sep 12;1353(3):298-306. doi: 10.1016/s0167-4781(97)00105-x.
Plasmid DNA in exponentially growing Escherichia coli immediately relaxes after heat shock but the relaxed DNA re-supercoils rapidly, the despite continued presence of the heat shock conditions. We have now obtained genetic evidence indicating that the histone-like protein HU of E. coli is required for this re-supercoiling of DNA. Plasmid DNA in a hupA-hupB double gene-disruption mutant relaxed excessively after heat shock, while the relaxation of DNA in a himA-himD double gene-disruption mutant and in an hns insertion mutant was transient, thereby indicating that HU protein, but not IHF or H-NS proteins, is required for the re-supercoiling of DNA. Exposure of the hupA-hupB double mutant to a temperature of 50 degrees C led to both excessive relaxation of DNA and to a decrease in viable cell number but temperatures lower than 46 degrees C did not lead to these events. Based on these results, we propose that HU protein maintains the negative supercoiling of DNA during thermal stress and contributes to cellular thermotolerance in E. coli.
处于指数生长期的大肠杆菌中的质粒DNA在热休克后立即松弛，但尽管热休克条件持续存在，松弛的DNA会迅速重新超螺旋化。我们现在已经获得了遗传证据，表明大肠杆菌的类组蛋白HU蛋白是DNA这种重新超螺旋化所必需的。hupA-hupB双基因破坏突变体中的质粒DNA在热休克后过度松弛，而himA-himD双基因破坏突变体和hns插入突变体中DNA的松弛是短暂的，从而表明DNA重新超螺旋化需要HU蛋白，而不是IHF或H-NS蛋白。将hupA-hupB双突变体暴露于50摄氏度的温度下会导致DNA过度松弛和活细胞数量减少，但低于46摄氏度的温度不会导致这些情况。基于这些结果，我们提出HU蛋白在热应激期间维持DNA的负超螺旋，并有助于大肠杆菌的细胞耐热性。
