Arsenic sensing and resistance system in the cyanobacterium Synechocystis sp strain PCC 6803
Arsenic sensing and resistance system in the cyanobacterium Synechocystis sp strain PCC 6803
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DOI：
10.1128/jb.185.18.5363-5371.2003
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发表时间：
2003-09-01
影响因子：
3.2
通讯作者：
Reyes, JC
中科院分区：
文献类型：
--
作者：
López-Maury, L;Florencio, FJ;Reyes, JC
砷是全球最重要的环境污染物之一。在这里，我们表明，蓝藻集胞藻属。菌株PCC 6803含有一个砷和锑抗性操纵子由三个基因组成：arsB，编码一个假定的亚砷酸盐和亚锑酸盐载体，arsH，编码一个未知功能的蛋白质，和arsC，编码一个假定的砷酸盐还原酶。而arsB突变株敏感的亚砷酸盐，砷酸盐和亚锑酸盐，arsC突变体只敏感的砷酸盐。arsH突变株在试验条件下未表现出明显的表型。在体内，arsBHC操纵子被砷和锑（氧化态，+3）的含氧阴离子去抑制，在较小程度上，被铋（氧化态，+3）和砷酸盐（氧化态，+5）去抑制。在没有这些效应子的情况下，操纵子被ArsR/SmtB家族的转录阻遏物抑制，该转录阻遏物由称为arsR的非连锁基因编码。因此，arsR无效突变体显示arsBHC操纵子的组成性去阻遏。砷或锑化合物的存在下，arsR基因的表达没有改变。纯化的重组ArsR蛋白在不存在金属的情况下与arsBHC启动子-操纵基因区结合，在存在Sb（III）或As（III）的情况下与DNA解离，但在存在As（V）的情况下则不解离，这表明三价类金属是真正的诱导剂系统。DNA酶I足迹实验表明，ArsR结合到两个17-bp的直接重复序列，每个重复序列由两个反向重复序列组成，在arsBHC启动子-操纵子的核苷酸-34至+17的区域。
Arsenic is one of the most important global environmental pollutants. Here we show that the cyanobacterium Synechocystis sp. strain PCC 6803 contains an arsenic and antimony resistance operon consisting of three genes: arsB, encoding a putative arsenite and antimonite carrier, arsH, encoding a protein of unknown function, and arsC, encoding a putative arsenate reductase. While arsB mutant strains were sensitive to arsenite, arsenate, and antimonite, arsC mutants were sensitive only to arsenate. The arsH mutant strain showed no obvious phenotype under the conditions tested. In vivo the arsBHC operon was derepressed by oxyanions of arsenic and antimony (oxidation state, +3) and, to a lesser extent, by bismuth (oxidation state, +3) and arsenate (oxidation state, +5). In the absence of these effectors, the operon was repressed by a transcription repressor of the ArsR/SmtB family, encoded by an unlinked gene termed arsR. Thus, arsR null mutants showed constitutive derepression of the arsBHC operon. Expression of the arsR gene was not altered by the presence of arsenic or antimony compounds. Purified recombinant ArsR protein binds to the arsBHC promoter-operator region in the absence of metals and dissociates from the DNA in the presence of Sb(III) or As(III) but not in the presence of As(V), suggesting that trivalent metalloids are the true inducers of the system. DNase I footprinting experiments indicate that ArsR binds to two 17-bp direct repeats, with each one consisting of two inverted repeats, in the region from nucleotides -34 to + 17 of the arsBHC promoter-operator.