López-Maury Luis, García-Domínguez Mario, Florencio Francisco J, Reyes José C
Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, E-41092 Sevilla, Spain.
Mol Microbiol. 2002 Jan;43(1):247-56. doi: 10.1046/j.1365-2958.2002.02741.x.
In the cyanobacterium Synechocystis sp. PCC 6803, genes for Ni2+, Co2+, and Zn2+ resistance are grouped in a 12 kb gene cluster. The nrsBACD operon is composed of four genes, which encode proteins involved in Ni2+ resistance. Upstream from nrsBACD, and in opposite orientation, a transcription unit formed by the two genes rppA and rppB has been reported previously to encode a two-component signal transduction system involved in redox sensing. In this report, we demonstrate that rppA and rppB (here redesigned nrsR and nrsS respectively) control the Ni2+-dependent induction of the nrsBACD operon and are involved in Ni2+ sensing. Thus, expression of the nrsBACD operon was not induced by Ni2+ in a nrsRS mutant strain. Furthermore, nrsRS mutant cells showed reduced tolerance to Ni2+. Whereas the nrsBACD operon is transcribed from two different promoters, one constitutive and the other dependent on the presence of Ni2+ in the medium, the nrsRS operon is transcribed from a single Ni2+-inducible promoter. The nrsRS promoter is silent in a nrsRS mutant background suggesting that the system is autoregulated. Purified full length NrsR protein is unable to bind to the nrsBACD-nrsRS intergenic region; however, an amino-terminal truncated protein that contains the DNA binding domain of NrsR binds specifically to this region. Our nrsRS mutant, which carries a deletion of most of the nrsR gene and part of the nrsS gene, does not show redox imbalance or photosynthetic gene mis-expression, contrasting with the previously reported nrsR mutant.
在蓝藻集胞藻PCC 6803中，负责镍离子、钴离子和锌离子抗性的基因成簇排列在一个12 kb的基因簇中。nrsBACD操纵子由四个基因组成，它们编码参与镍离子抗性的蛋白质。先前报道，在nrsBACD上游且方向相反的位置，由rppA和rppB这两个基因组成的转录单元编码一个参与氧化还原感应的双组分信号转导系统。在本报告中，我们证明rppA和rppB（此处分别重新命名为nrsR和nrsS）控制nrsBACD操纵子的镍离子依赖性诱导，并参与镍离子感应。因此，在nrsRS突变株中，镍离子不会诱导nrsBACD操纵子的表达。此外，nrsRS突变细胞对镍离子的耐受性降低。nrsBACD操纵子从两个不同的启动子转录，一个是组成型的，另一个依赖于培养基中镍离子的存在，而nrsRS操纵子从单个镍离子诱导型启动子转录。nrsRS启动子在nrsRS突变背景中是沉默的，这表明该系统是自动调节的。纯化的全长NrsR蛋白无法结合到nrsBACD - nrsRS基因间区域；然而，包含NrsR DNA结合结构域的氨基末端截短蛋白能特异性结合该区域。我们的nrsRS突变体缺失了大部分nrsR基因和部分nrsS基因，与先前报道的nrsR突变体不同，它没有表现出氧化还原失衡或光合基因表达异常。
