de Lorenzo V, Pérez-Martín J
Centro Nacional de Biotechnología (CSIC), Madrid, Spain. VDLORENZO
Mol Microbiol. 1996 Mar;19(6):1177-84. doi: 10.1111/j.1365-2958.1996.tb02463.x.
Various features of the regulation of pathways for biodegradation of recalcitrant compounds by Pseudomonas provide insights into the mechanisms by which operons evolve to acquire conditionally active promoters that permit the corresponding genes to be transcribed only when required. The "regulatory noise hypothesis' proposes that transcriptional control systems develop responsiveness to new signals due to the leakiness and lack of specificity of preexisting promoters and regulators. When needed, these may become more specific through suppression of undesirable signals and further fine-tuning of the recruited proteins to interact with distinct chemicals. This hypothesis is supported by the sophisticated regulation of sigma 54-dependent promoters of the TOL (toluene biodegradation) operons, which can be activated to various degrees by heterologous proteins. Such "illegitimate' activation is suppressed by bent DNA structures, either static or protein induced, between promoter core elements. Therefore, not only the regulators but also the DNA sequences participate in the process that gives rise to novel specificities.
假单胞菌对难降解化合物生物降解途径的调控具有多种特征，这为操纵子如何进化以获得条件活性启动子提供了见解，这些启动子使得相应基因仅在需要时才被转录。“调控噪声假说”提出，由于现有启动子和调节因子的泄漏性和缺乏特异性，转录控制系统会发展出对新信号的响应能力。在需要时，这些系统可以通过抑制不期望的信号以及对募集的蛋白质进行进一步微调以与不同化学物质相互作用而变得更加特异。这一假说得到了TOL（甲苯生物降解）操纵子中依赖σ54的启动子复杂调控的支持，这些启动子可被异源蛋白不同程度地激活。这种“非法”激活被启动子核心元件之间静态的或蛋白质诱导的弯曲DNA结构所抑制。因此，不仅调节因子，而且DNA序列也参与了产生新特异性的过程。
