Heavy-metal-ion- (Cd2+, Cu2+, Pb2+, Hg2+ and Zn2+) or heat (50 degrees C)-stress treatments of the unicellular cyanobacterium Synechococcus sp., strain PCC 6301, under both light and dark conditions led to the accumulation of bis(5′-nucleosidyl)oligophosphates: Ap4A, Ap4G, Ap3A, Ap3G and Ap3Gp2. Under light regimens, the accumulation of Ap4A and Ap4G is more characteristic of heavy-metal-ion-stressed cells, whereas the accumulation of Ap3A, Ap3G and Ap3Gp2 is the dominant feature of heavy-metal-ion or heat-shock treatment during energy deprivation (i.e. in the dark). This accumulation of bisnucleoside oligophosphates supports a model whereby the adenylylated nucleotides are synthesized by the backward reaction of tRNA-aminoacyl synthetases. These nucleotides may also act to switch or modulate cyanobacterial responses under various environmental stress conditions.
