Mercury (Hg) is a highly toxic and widely distributed heavy metal which some Bacteria and Archaea detoxify by the reduction of ionic Hg (Hg[II]) to the elemental volatile form, Hg(0). This activity is specified by the mer operon. The mer operon of the deeply-branching thermophile Thermus thermophilus HB27 encodes for, an O-acetyl-L-homoacetylserine sulfhydrylase (Oah2), a transcriptional regulator (MerR), a hypothetical protein (hp), and a mercuric reductase (MerA). Here we show that this operon has two convergently-expressed and differentially-regulated promoters. An upstream promoter, Poah , controls the constitutive transcription of the entire operon and a second promoter (Pmer ), located within merR, is responsive to Hg(II). In the absence of Hg(II), the transcription of merA is basal and when Hg(II) is present, merA transcription is induced. This response to Hg(II) is controlled by MerR and genetic evidence suggests that MerR acts as a repressor and activator of Pmer . When the whole merR, including Pmer , is removed, merA is transcribed from Poah independently of Hg(II). These results suggest that the transcriptional regulation of mer in T. thermophilus is both similar to, and different from, the well-documented regulation of proteobacterial mer systems, possibly representing an early step in the evolution of mer-operon regulation. This article is protected by copyright. All rights reserved.

中文翻译：

---

mer operon在嗜热栖热菌中的表达和调控。

汞（Hg）是一种剧毒且分布广泛的重金属，某些细菌和古细菌通过将离子性Hg（Hg [II]）还原为元素挥发性形式Hg（0）来解毒。此活动由mer操纵子指定。嗜热嗜热菌Thermus thermophilus HB27的mer操纵子编码为O-乙酰基-L-高乙酰丝氨酸丝氨酸巯基化酶（Oah2），转录调节子（MerR），假设蛋白（hp）和汞还原酶（MerA）。在这里，我们显示该操纵子具有两个收敛表达和差异调控的启动子。上游启动子Poah控制整个操纵子的组成型转录，位于merR内的第二个启动子（Pmer）对Hg（II）有反应。在没有Hg（II）的情况下，merA的转录是基础的，当存在Hg（II）时，会诱导merA转录。对Hg（II）的反应受MerR控制，遗传证据表明MerR充当Pmer的阻遏物和激活物。当去除整个merR（包括Pmer）时，merA会独立于Hg（II）从Poah转录。这些结果表明，嗜热链球菌中mer的转录调控既与证明良好的变形细菌mer系统的调控相似，又与之不同，可能代表了mer-operon调控进化的第一步。本文受版权保护。版权所有。这些结果表明，嗜热链球菌中mer的转录调控既与证明良好的变形细菌mer系统的调控相似，又与之不同，可能代表了mer-operon调控进化的第一步。本文受版权保护。版权所有。这些结果表明，嗜热链球菌中mer的转录调控既与证明良好的变形细菌mer系统的调控相似，又与之不同，可能代表了mer-operon调控进化的第一步。本文受版权保护。版权所有。