López-Maury Luis, Florencio Francisco J, Reyes José C
Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas, Universidad de Sevilla, E-41092 Seville, Spain.
J Bacteriol. 2003 Sep;185(18):5363-71. doi: 10.1128/JB.185.18.5363-5371.2003.
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.
砷是全球最重要的环境污染物之一。在此我们表明，集胞藻属蓝细菌PCC 6803菌株含有一个抗砷和抗锑操纵子，该操纵子由三个基因组成：arsB，编码一种假定的亚砷酸盐和亚锑酸盐载体；arsH，编码一种功能未知的蛋白质；arsC，编码一种假定的砷酸盐还原酶。虽然arsB突变菌株对亚砷酸盐、砷酸盐和亚锑酸盐敏感，但arsC突变体仅对砷酸盐敏感。arsH突变菌株在测试条件下未表现出明显表型。在体内，arsBHC操纵子受到砷和锑的氧阴离子（氧化态为+3）以及程度较轻的铋（氧化态为+3）和砷酸盐（氧化态为+5）的去阻遏作用。在没有这些效应物的情况下，该操纵子受到由一个不连锁基因arsR编码的ArsR/SmtB家族转录阻遏物的抑制。因此，arsR缺失突变体表现出arsBHC操纵子的组成型去阻遏。arsR基因的表达不受砷或锑化合物存在的影响。纯化的重组ArsR蛋白在没有金属的情况下与arsBHC启动子 - 操纵子区域结合，在存在Sb(III)或As(III)时从DNA上解离，但在存在As(V)时不解离，这表明三价类金属是该系统的真正诱导物。DNase I足迹实验表明，ArsR在arsBHC启动子 - 操纵子核苷酸 -34至 +17区域结合到两个17 bp的直接重复序列上，每个直接重复序列由两个反向重复序列组成。
