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

Summary In the cyanobacterium Synechocystis sp. PCC 6803, genes for Ni 2 + , Co 2 + , and Zn 2 + resistance are grouped in a 12 kb gene cluster. The nrsBACD operon is composed of four genes, which encode proteins involved in Ni 2 + 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 Ni 2 + ‐dependent induction of the nrsBACD operon and are involved in Ni 2 + sensing. Thus, expression of the nrsBACD operon was not induced by Ni 2 + in a nrsRS mutant strain. Furthermore, nrsRS mutant cells showed reduced tolerance to Ni 2 + . Whereas the nrsBACD operon is transcribed from two different promoters, one constitutive and the other dependent on the presence of Ni 2 + in the medium, the nrsRS operon is transcribed from a single Ni 2 + ‐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.