Copper-mediated regulation of cytochrome c553 and plastocyanin in the cyanobacterium Synechocystis 6803

In certain cyanobacteria and algae, cytochrome or plastocyanin can serve to carry electrons from the cytochrome bf complex to photosystem I. The availability of copper in the growth medium regulates which protein is present. To investigate copper induced control of gene expression we isolated these proteins from the cyanobacterium Synechocystis 6803. Using immunodetection and optical spectroscopy, the steady state levels of cytochrome c(553) and plastocyanin were measured in cells grown at different copper concentrations. The results show that in cells grown in 20-30 nm copper, cytochrome c(553) was present, whereas plastocyanin was not detected. The opposite behavior was observed in cells grown in the presence of 1 micromolar copper; plastocyanin was present, whereas cytochrome could not be detected. Both proteins were present in cells grown in 0.3 micromolar copper. Northern analysis of total RNA, probed with a gene fragment for cytochrome c(553) or the plastocyanin gene, showed that cells grown in the presence of 20-30 nm copper have message for cytochrome c(553), but not for plastocyanin, whereas cells grown in 1 micromolar copper have message for plastocyanin, but not for cytochrome c(553). These results demonstrate that copper regulates expression of both of the genes encoding cytochrome c(553) and plastocyanin prior to translation in Synechocystis 6803