Division of Biology, Faculty of Natural Sciences, Sir Alexander Fleming Building, Imperial College London, London SW7 2AZ, UK.
Nat Commun. 2011 Feb 1;2:177. doi: 10.1038/ncomms1177.
The bacterial AAA+ enhancer-binding proteins (EBPs) HrpR and HrpS (HrpRS) of Pseudomonas syringae (Ps) activate σ(54)-dependent transcription at the hrpL promoter; triggering type-three secretion system-mediated pathogenicity. In contrast with singly acting EBPs, the evolution of the strictly co-operative HrpRS pair raises questions of potential benefits and mechanistic differences this transcription control system offers. Here, we show distinct properties of HrpR and HrpS variants, indicating functional specialization of these non-redundant, tandemly arranged paralogues. Activities of HrpR, HrpS and their control proteins HrpV and HrpG from Ps pv. tomato DC3000 in vitro establish that HrpRS forms a transcriptionally active hetero-hexamer, that there is a direct negative regulatory role for HrpV through specific binding to HrpS and that HrpG suppresses HrpV. The distinct HrpR and HrpS functionalities suggest how partial paralogue degeneration has potentially led to a novel control mechanism for EBPs and indicate subunit-specific roles for EBPs in σ(54)-RNA polymerase activation.
丁香假单胞菌（Ps）的细菌 AAA+增强子结合蛋白（EBPs）HrpR 和 HrpS（HrpRS）激活 hrpL 启动子的 σ(54)-依赖性转录；触发 III 型分泌系统介导的致病性。与单一作用的 EBPs 不同，严格合作的 HrpRS 对的进化提出了关于这种转录控制系统提供的潜在益处和机制差异的问题。在这里，我们展示了 HrpR 和 HrpS 变体的不同特性，表明这些非冗余、串联排列的同源物具有功能专业化。来自 Ps pv 的 HrpR、HrpS 及其调控蛋白 HrpV 和 HrpG 的活性。番茄 DC3000 在体外建立了 HrpRS 形成转录活性的异六聚体，HrpV 通过特异性结合 HrpS 对 HrpS 具有直接的负调控作用，而 HrpG 抑制 HrpV。HrpR 和 HrpS 的不同功能表明部分同源物退化如何可能导致 EBPs 的新型调控机制，并指出 EBPs 在 σ(54)-RNA 聚合酶激活中的亚基特异性作用。
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