Molecular mechanism of the primary step of heat shock response

对环境压力的良好协调的细胞反应对于生存和维持健康生命至关重要。近年来，对热休克反应的分子调控机制的研究取得了很大进展，其中以大肠杆菌为研究对象的研究起到了基础性和先导性的作用。热休克处理引起细胞内RNA聚合酶亚基σ ^的浓度增加<32>，从而诱导一组编码所谓热休克蛋白的基因的表达（通过转录），如分子伴侣GroE、DnaJ、DnaK、GrpE等。我们最近对σ ^浓度增加的分析<32>表明，异常蛋白的积累导致原本不稳定的σ ^<32>变得稳定。然而，它并没有增加sigma合成的速率<32>。我们的研究结果表明，有至少两个不同的途径增加σ ^<32>浓度。其中一条是通过异常蛋白质积累的稳定化途径，另一条是刺激sigma^合成的途径<32>，对于后者，我们已经证明了编码sigma^的rpoH基因转录的二级结构mRNA的参与<32>。我们怀疑还有反式作用因子，因此我们致力于通过设计一种突变选择方法来寻找它们。对于前一种途径，我们通过定点突变技术分析sigma^的结构域结构<32>，以确定sigma^稳定化的调节机制<32>。

The well-coordinated cellular response to the environmental stresses is essential for survival and maintenance of healthy life. Our understanding of the molecular regulatory mechanism of heat-shock response has been advanced by recent active investigations, among which studies with Escherichia coli has playd a role of providing basic and leading contributions. A heat-shock treatment triggers an increase of the cellular concentration of an RNA polymerase subunit sigma^<32>, which them induces expression(by transcription)of a group of genes coding for so-called heat-shock proteins such as the molecular chaperones GroE, DnaJ, DnaK, GrpE, and so on.Our recent ayalysis about the increase of the sigma^<32> concentration revealed that accmulation of abnormal proteins led the otherwise unstable sigma^<32> to become stable. It, however, did not increase the rate of sigma^<32> synthesis. Our results imply that there are at least two distinct pathways for the increase of sigma^<32> concentration. One is the stabilization pathway through accumulation of abnormal proteins, and the other is a pathway for stimulating sigma^<32> synthesis.For the latter pathway, we have shown the participation of the secondary structure mRNA transcribed from the rpoH gene encoding sigma^<32>. We suspect that there are in addition trans-acting factors ; thus we are engaged in finding them by devising a mutant-selection method.For the former pathway, we are analysing the domain structure of sigma^<32> by a site-directed-mutagenesis technique to determine the regulatory mechanism for the sigma^<32> stabilization.