The UzcRS two-component system integrates regulatory input from a diverse set of auxiliary regulators. The UzcRS two-component system integrates regulatory input from a diverse set of auxiliary regulators

The UzcRS two-component system in Caulobacter crescentus functions as a global activator of an extracytoplasmic stress response pathway and is induced by the metals U, Zn and Cu. Unexpectedly, a screen for mutations that affected the activity of the UzcR-regulated urcA promoter (PurcA) revealed four previously uncharacterized proteins whose inactivation led to metal-independent induction of PurcA. Using molecular genetics and functional genomics, we found that these auxiliary regulators regulate PurcA expression by modulating the activity of UzcRS through distinct mechanisms. The membrane protein UzcX, whose expression is positively regulated by UzcR, forms a regulatory complex with UzcS, providing a mechanism of feedback inhibition within the UzcRS circuit. UrtAP, an ABC transporter with a periplasmic metallo-aminopeptidase domain, negatively regulates UzcRS activity and antagonizes metal dependent stimulation by virtue of its enzymatic activity. Lastly, two MarR family transcription factors, MarR1 and MarR2, synergistically regulate UzcRS activity by repressing the expression of the membrane proteins UzcY and UzcZ, respectively, which function as UzcRS activators. In addition to modulating basal UzcRS activity, UzcY and UzcZ enhance the U/Zn/Cu sensitivity of UzcRS, shifting its responsiveness to more environmentally-relevant metal concentrations. Collectively, these data suggest that UzcRS functions as the core-signaling unit within a multicomponent signal transduction pathway that includes an unusually diverse set of auxiliary regulators. Overall design: Gene expression profiles of ΔuzcR, ΔuzcX ΔuzcR, ΔurtAP ΔuzcR, ΔmarR1 ΔuzcR, ΔmarR2 ΔuzcR strains were determined in triplicate

新月柄杆菌（Caulobacter crescentus）中的UzcRS双组分系统（two-component system）是胞外应激反应通路的全局激活因子，可被金属铀（U）、锌（Zn）和铜（Cu）诱导激活。出乎意料的是，通过对影响UzcR调控的urcA启动子（PurcA）活性的突变体进行遗传筛选，我们发现了4种此前未被表征的蛋白质，它们的失活会导致PurcA出现非金属依赖的诱导表达。借助分子遗传学与功能基因组学手段，我们发现这些辅助调控因子可通过不同的调控机制，调节UzcRS的活性，进而调控PurcA的表达。膜蛋白UzcX的表达受UzcR正调控，它可与UzcS形成调控复合物，为UzcRS信号回路内的反馈抑制提供了分子机制。UrtAP是带有周质金属氨肽酶结构域的ATP结合盒转运蛋白（ABC transporter），它可负调控UzcRS的活性，并凭借自身的酶活拮抗金属依赖的信号刺激。最后，两种MarR家族转录因子（MarR1和MarR2）可分别抑制膜蛋白UzcY和UzcZ的表达，进而协同调控UzcRS的活性；而UzcY和UzcZ本身作为UzcRS的激活因子发挥功能。除了调节UzcRS的基础活性外，UzcY和UzcZ还能增强UzcRS对U、Zn、Cu的敏感性，将其响应阈值调整至更符合环境实际存在的金属浓度范围。综合来看，这些数据表明，UzcRS是多组分信号转导通路中的核心信号单元，该通路包含了一套异常多样的辅助调控因子。实验整体设计：对ΔuzcR、ΔuzcX ΔuzcR、ΔurtAP ΔuzcR、ΔmarR1 ΔuzcR、ΔmarR2 ΔuzcR这5种缺失突变株的基因表达谱进行了三次生物学重复检测。