A two‐component signal transduction system involved in nickel sensing in the cyanobacterium Synechocystis sp. PCC 6803

Abstract

Summary 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.

Gene expression under low-oxygen conditions in the cyanobacterium Synechocystis sp. PCC 6803 demonstrates Hik31-dependent and -independent responses

“…These genes included sll0797 and sll0798 that encode a two-component system with multiple regulatory roles responding to Ni 2+ , cellular redox and inorganic carbon availability (Li & Sherman, 2000;Ló pez-Maury et al, 2002;Wang et al, 2004a). The gene slr1285 that encodes Hik34 was also downregulated in the wild-type.…”

The Histidine Kinase Hik34 Is Involved in Thermotolerance by Regulating the Expression of Heat Shock Genes in Synechocystis

“…The chromosome of Synechocystis includes 44 putative genes for Hiks that are candidates for sensors of environmental signals Mizuno et al, 1996). It has already been demonstrated that the Hiks in Synechocystis are involved in the perception and transduction of signals due to cold stress (Suzuki et al, 2000, phosphate deprivation (Hirani et al, 2001;Suzuki et al, 2004), high osmolarity Paithoonrangsarid et al, 2004), heavy metal ions (Ló pez-Maury et al, 2002;Ogawa et al, 2002;Yamaguchi et al, 2002), and high concentrations of NaCl (Marin et al, 2003). In this article, we provide evidence that Hik34, one of the 44 putative Hiks in Synechocystis, is involved in the control of the expression of heat shock genes and the regulation of thermotolerance in Synechocystis.…”

Function of the N-terminal region of the phosphate-sensing histidine kinase, SphS, in Synechocystis sp. PCC 6803

“…To investigate the dependence of the specific amino acid sequence of the SphS hydrophobic domain on kinase activation and sensing we decided to completely replace this region with the amino acid sequence from the Ni 2+ -sensing histidine kinase NrsS (Lopez-Maury et al, 2002). These two hydrophobic regions have very little amino acid sequence similarity (see Supplementary Fig.…”