A two-component signal transduction system involved in nickel sensing in the cyanobacterium XXXX .

@entity8862 @entity1472 @entity515 @entity3411 @entity324
In the cyanobacterium @entity324 , genes for @entity3411 , @entity515 , and @entity8862 resistance are grouped in a 12 kb gene cluster. The nrsBACD operon is composed of four genes, which encode proteins involved in @entity3411 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 @entity3411 -dependent induction of the nrsBACD operon and are involved in @entity3411 sensing. Thus, expression of the nrsBACD operon was not induced by @entity3411 in a nrsRS mutant strain. Furthermore, nrsRS mutant cells showed reduced tolerance to @entity3411 . Whereas the nrsBACD operon is transcribed from two different promoters, one constitutive and the other dependent on the presence of @entity3411 in the medium, the nrsRS operon is transcribed from a single @entity3411 -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 @entity1472 -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.
