Holtmann Gudrun, Brigulla Matthias, Steil Leif, Schütz Alexandra, Barnekow Karsta, Völker Uwe, Bremer Erhard
Laboratory for Microbiology, Department of Biology, Philipps-University Marburg, Karl-von-Frisch-Str., D-35032 Marburg, Federal Republic of Germany.
J Bacteriol. 2004 Sep;186(18):6150-8. doi: 10.1128/JB.186.18.6150-6158.2004.
General stress proteins protect Bacillus subtilis cells against a variety of environmental insults. This adaptive response is particularly important for nongrowing cells, to which it confers a multiple, nonspecific, and preemptive stress resistance. Induction of the general stress response relies on the alternative transcription factor, SigB, whose activity is controlled by a partner switching mechanism that also involves the anti-sigma factor, RsbW, and the antagonist protein, RsbV. Recently, the SigB regulon has been shown to be continuously induced and functionally important in cells actively growing at low temperature. With the exception of this chill induction, all SigB-activating stimuli identified so far trigger a transient expression of the SigB regulon that depends on RsbV. Through a proteome analysis and Northern blot and gene fusion experiments, we now show that the SigB regulon is continuously induced in cells growing actively at 51 degrees C, close to the upper growth limit of B. subtilis. This heat induction of SigB-dependent genes requires the environmental stress-responsive phosphatase RsbU, but not the metabolic stress-responsive phosphatase RsbP. RsbU dependence of SigB activation by heat is overcome in mutants that lack RsbV. In addition, loss of RsbV alone or in combination with RsbU triggers a hyperactivation of the general stress regulon exclusively at high temperatures detrimental for cell growth. These new facets of heat induction of the SigB regulon indicate that the current view of the complex genetic and biochemical regulation of SigB activity is still incomplete and that SigB perceives signals independent of the RsbV-mediated signal transduction pathways under heat stress conditions.
一般应激蛋白可保护枯草芽孢杆菌细胞免受多种环境损伤。这种适应性反应对于不生长的细胞尤为重要,赋予它们多重、非特异性和先发制人的应激抗性。一般应激反应的诱导依赖于替代转录因子SigB,其活性由一种伴侣切换机制控制,该机制还涉及抗σ因子RsbW和拮抗蛋白RsbV。最近,已证明SigB调控子在低温下活跃生长的细胞中持续被诱导且具有重要功能。除了这种冷诱导外,迄今为止鉴定出的所有激活SigB的刺激都触发了依赖于RsbV的SigB调控子的瞬时表达。通过蛋白质组分析、Northern印迹和基因融合实验,我们现在表明SigB调控子在51摄氏度下活跃生长的细胞中持续被诱导,该温度接近枯草芽孢杆菌的生长上限。这种对SigB依赖性基因的热诱导需要环境应激反应性磷酸酶RsbU,但不需要代谢应激反应性磷酸酶RsbP。在缺乏RsbV的突变体中,热对SigB激活的RsbU依赖性被克服。此外,单独缺失RsbV或与RsbU一起缺失仅在对细胞生长有害的高温下触发一般应激调控子的过度激活。SigB调控子热诱导的这些新方面表明,目前对SigB活性复杂遗传和生化调控的看法仍然不完整,并且在热应激条件下SigB可感知独立于RsbV介导的信号转导途径的信号。