Abstract
PII protein, conserved in Bacteria, Archaea, and Plant, functions as a sensor of carbon/nitrogen ratio. Under nitrogen starvation, PII covalently binds with 2-oxoglutarate (2-OG), and then the serine residue is phosphorylated. Using yeast two-hybrid screening with Synechocystis PCC6803 genomic library, we identified a novel PII binding protein, named PamA, and demonstrated that PamA interacts with PII in vitro, although dissociated under the presence of ATP and 2-OG (Osanai et al. 2003). pamA deletion mutant (GN10) exhibited the decreased mRNA of several nitrogen-related genes such as nitrogen-related group 2 sigma factor sigE. By the classification of nitrogen-related genes based on transcriptional analyses using GN10, we found that PamA is only responsible for the transcriptions of nitrogen-related genes expressed from the phase-II of nitrogen limitation. These results suggest that cyanobacteria retain transcriptional cascades under nitrogen starvation and PamA is involved in the expressions of phase-II nitrogen-related genes.
