da Silva Antonio C A, Simão Rita C G, Susin Michelle F, Baldini Regina L, Avedissian Marcelo, Gomes Suely L
Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, C. P. 26077, São Paulo, SP, 05513-970, Brazil.
Mol Microbiol. 2003 Jul;49(2):541-53. doi: 10.1046/j.1365-2958.2003.03581.x.
Expression of heat shock genes in Gram-negative proteobacteria is positively modulated by the transcriptional regulator RpoH, the sigma(32) subunit of RNA polymerase (RNAP). In this study we investigated the chaperones DnaK/DnaJ and GroES/GroEL as possible modulators of the heat response in Caulobacter crescentus. We have shown that cells overexpressing DnaK show poor induction of heat shock protein (HSP) synthesis, even though sigma(32) levels present a normal transient increase upon heat stress. On the other hand, depletion of DnaK led to higher levels of sigma(32) and increased transcription of HSP genes, at normal growth temperature. In contrast, changes in the amount of GroES/EL had little effect on sigma(32) levels and HSP gene transcription. Despite the strong effect of DnaK levels on the induction phase of the heat shock response, downregulation of HSP synthesis was not affected by changes in the amount this chaperone. Thus, we propose that competition between sigma(32) and sigma(73), the major sigma factor, for the core RNAP could be the most important factor controlling the shut-off of HSP synthesis during recovery phase. In agreement with this hypothesis, we have shown that expression of sigma(73) gene is heat shock inducible.
革兰氏阴性变形杆菌中热休克基因的表达受到转录调节因子RpoH（RNA聚合酶（RNAP）的σ32亚基）的正向调节。在本研究中，我们研究了伴侣蛋白DnaK/DnaJ和GroES/GroEL作为新月柄杆菌热反应可能调节因子的作用。我们发现，过表达DnaK的细胞对热休克蛋白（HSP）合成的诱导较差，尽管在热应激时σ32水平呈现正常的短暂升高。另一方面，在正常生长温度下，DnaK的缺失导致σ32水平升高和HSP基因转录增加。相比之下，GroES/EL数量的变化对σ32水平和HSP基因转录影响很小。尽管DnaK水平对热休克反应的诱导阶段有强烈影响，但HSP合成的下调不受该伴侣蛋白数量变化的影响。因此，我们提出，σ32和主要的σ因子σ73之间对核心RNAP的竞争可能是控制恢复阶段HSP合成关闭的最重要因素。与这一假设一致，我们发现σ73基因的表达是热休克诱导型的。
