A two-component signal transduction system involved in nickel sensing in the cyanobacterium Synechocystis sp. PCC 6803.
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.
López-Maury
Luis
L
Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, E-41092 Sevilla, Spain.
García-Domínguez
Mario
M
Florencio
Francisco J
FJ
Reyes
José C
JC
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D000458:Cyanobacteria / Q000187:drug effects / Q000235:genetics*; D015870:Gene Expression; D008969:Molecular Sequence Data; D009532:Nickel / Q000494:pharmacology*; D009876:Operon; D010788:Photosynthesis; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction
D001426:Bacterial Proteins; C412036:RppA protein, Synechocystis; C029938:nickel sulfate; D009532:Nickel