Control of a programmed cell death pathway in Pseudomonas aeruginosa by a ppGpp-responsive antiterminator [RNA-Seq]. Control of a programmed cell death pathway in Pseudomonas aeruginosa by a ppGpp-responsive antiterminator [RNA-Seq]

In the opportunistic pathogen Pseudomonas aeruginosa the alp system encodes a programmed cell death (PCD) pathway that is switched on in a subset of cells in response to DNA damage. Here we show that the central regulator of this pathway, AlpA, exerts its effects by acting as an antiterminator rather than a transcription activator. In particular, we present evidence that AlpA positively regulates the alpBCDE cell lysis genes, as well as genes in a second newly identified operon, by recognizing specific DNA sites within the promoter, then binding RNA polymerase directly and allowing it to bypass intrinsic terminators positioned downstream. We further show that the activity of AlpA is potentiated by the alarmone ppGpp, which is produced by the cell in response to stress. Through its responsiveness to ppGpp, AlpA can integrate environmental cues into the decision to execute a PCD pathway that is linked to the virulence of the organism. Overall design: Comparison of transcripts between wild-type Pseudomonas aeruginosa PAO1 ectopically expressing AlpA compared to empty vector control and the same comparison in cells lacking relA

在机会致病菌铜绿假单胞菌（Pseudomonas aeruginosa）中，alp系统编码一条程序性细胞死亡（programmed cell death, PCD）通路，该通路可在部分细胞中响应DNA损伤而被激活。本研究揭示，该通路的核心调控因子AlpA并非以转录激活因子（transcription activator）的身份发挥作用，而是作为抗终止因子（antiterminator）行使功能。具体而言，我们通过实验证据证实，AlpA可识别启动子（promoter）内的特定DNA位点，随后直接结合RNA聚合酶（RNA polymerase），使其绕过下游的内在终止子（intrinsic terminators），进而正向调控alpBCDE细胞裂解基因，以及第二个新发现的操纵子（operon）内的基因。我们进一步发现，AlpA的活性可被告警素（alarmone）ppGpp增强，而ppGpp是细胞响应胁迫时合成的信号分子。借助对ppGpp的响应性，AlpA能够整合环境信号，从而启动与该病原菌毒力相关的PCD通路。整体实验设计：对比异位表达AlpA的野生型铜绿假单胞菌PAO1与空载载体对照的转录本表达谱，同时在缺失relA基因（relA）的细胞中开展相同的对比实验。