Modification of the p_IIprotein in response to carbon and nitrogen availability in filamentous heterocystous cyanobacteria

Abstract

In the filamentous cyanobacterium <it>Calothrix</it> PCC 7504, which fixes N<inf>2</inf> aerobically, the modification state of the regulatory P<inf>II</inf> protein (GlnB) was shown to depend on nitrogen and carbon availability, as observed in the unicellular non-fixing strain <it>Synechococcus</it> PCC 7942. However, the conditions for modifications, the time dependence of the process and the electrophoretic behavior of the native P<inf>II</inf> isoforms differed somewhat between the two strains. In another strain, <it>Calothrix</it> PCC 7601, which has lost the capability to fix N<inf>2</inf>, P<inf>II</inf> was modified only if ammonia plus an inhibitor of glutamine synthetase were present. It is proposed that: (i) the behavior of the P<inf>II</inf> proteins depends upon the physiological properties of the strains; and (ii) the modification system of P<inf>II</inf> per se may differ between the two cyanobacterial genera.