Figure 1.

Northern-blot analysis of the ntcA gene expression in response to nitrogen source and availability. Total RNA was isolated from mid-log phase Synechocystis sp. PCC 6803 cells (A) that were grown during 12 h in medium containing NO₃⁻, NH₄⁺, or no nitrogen source. B, Nitrate-grown cells were harvested, washed, and transferred to nitrogen-free medium. Samples for RNA isolation were taken at the indicated times. Ten micrograms of total RNA was loaded per lane. Hybridization was performed with the ntcA gene probe. C, Cell extracts were obtained from cultures grown under the same conditions as in A, separated by SDS-PAGE, and western blot was carried out using polyclonal NtcA antiserum raised toward the recombinant Synechocystis sp. NtcA protein. Fifty micrograms of protein was loaded per lane.