Qi H, Menzel R, Tse-Dinh Y C
Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla 10595, USA.
Mol Microbiol. 1996 Aug;21(4):703-11. doi: 10.1046/j.1365-2958.1996.241390.x.
Topoisomerase I and DNA gyrase are the major topoisomerase activities responsible for the regulation of DNA supercoiling in the bacterium Escherichia coli. The P1 promoter of topA has previously been shown to be a delta 32-dependent heat-shock promoter. A mutant strain with a deletion of P1 was constructed. This mutant is > 10-fold more sensitive to heat treatment (52 degrees C) than the wild type. After brief treatment at 42 degrees C, wild-type Escherichia coli acquires an enhanced resistance to the effects of a subsequent 52 degrees C treatment. This is not the case for the P1 deletion mutant, which, and under these conditions, is about 100-fold less thermotolerant than the wild type. The presence of a plasmid expressing topoisomerase I restored the heat-survival level of the mutant to that of the wild type. During heat shock, the superhelical density of a plasmid with the heat-inducible rpoD promoter is increased in the P1 deletion mutant. We also note that the pulse-labelling pattern of proteins at 42 C (displayed on SDS-polyacrylamide gels) is different in the mutant, and, most notably, the amounts of DnaK and of GroEL protein are reduced. A model is proposed in order to unify these observations.
拓扑异构酶I和DNA促旋酶是负责调节大肠杆菌中DNA超螺旋的主要拓扑异构酶活性。topA的P1启动子先前已被证明是一种依赖δ32的热休克启动子。构建了一个缺失P1的突变菌株。该突变体对热处理（52℃）的敏感性比野生型高10倍以上。在42℃短暂处理后，野生型大肠杆菌对随后52℃处理的影响获得了增强的抗性。P1缺失突变体并非如此，在这些条件下，其耐热性比野生型低约100倍。表达拓扑异构酶I的质粒的存在将突变体的热存活水平恢复到野生型水平。在热休克期间，带有热诱导型rpoD启动子的质粒的超螺旋密度在P1缺失突变体中增加。我们还注意到，在42℃时蛋白质的脉冲标记模式（显示在SDS-聚丙烯酰胺凝胶上）在突变体中有所不同，最显著的是，DnaK和GroEL蛋白的量减少。为了统一这些观察结果，提出了一个模型。
