Single Transmembrane Peptide DinQ Modulates Membrane-Dependent Activities

The functions of several SOS regulated genes in Escherichia coli are still unknown, including dinQ. In this work we characterize dinQ and two small RNAs, agrA and agrB, with antisense complementarity to dinQ. Northern analysis revealed five dinQ transcripts, but only one transcript (+44) is actively translated. The +44 dinQ transcript translates into a toxic single transmembrane peptide localized in the inner membrane. AgrB regulates dinQ RNA by RNA interference to counteract DinQ toxicity. Thus the dinQ-agr locus shows the classical features of a type I TA system and has many similarities to the tisB-istR locus. DinQ overexpression depolarizes the cell membrane and decreases the intracellular ATP concentration, demonstrating that DinQ can modulate membrane-dependent processes. Augmented DinQ strongly inhibits marker transfer by Hfr conjugation, indicating a role in recombination. Furthermore, DinQ affects transformation of nucleoid morphology in response to UV damage. We hypothesize that DinQ is a transmembrane peptide that modulates membrane-dependent activities such as nucleoid compaction and recombination.大肠杆菌（Escherichia coli）中多个SOS调控基因的功能仍未阐明，dinQ便是其中之一。本研究对dinQ以及两条与dinQ存在反义互补序列的小RNA——agrA与agrB开展了功能表征。Northern印迹分析（Northern analysis）结果显示，dinQ可产生5种转录本，但仅+44转录本能够被主动翻译。该+44 dinQ转录本翻译得到一种毒性单次跨膜肽，定位于细胞内膜。AgrB可通过RNA干扰（RNA interference）调控dinQ RNA，以拮抗DinQ的毒性效应。据此，dinQ-agr基因座具备I型毒素-抗毒素（type I TA）系统的经典特征，且与tisB-istR基因座存在诸多相似性。DinQ过表达会引发细胞膜去极化，并降低细胞内ATP浓度，证实DinQ能够调控膜依赖型生理过程。过量DinQ会显著抑制高频重组（Hfr）接合介导的标记转移，表明其在重组过程中具有功能。此外，DinQ可影响紫外线（UV）损伤应答中的拟核形态重塑。我们推测，DinQ是一类跨膜肽，能够调控膜依赖型生理活动，例如拟核压缩与重组过程。