Abstract
In cyanobacteria, the genes related to nitrogen acquisition and metabolism are activated under nitrogen-limited conditions. In Synechococcus elongatus, one of the six genes encoding the group2 sigma factor of RNA polymerase, rpoD4, was also found to be upregulated by nitrogen limitation. The upregulation was partly (but not entirely) dependent on NtcA, the global nitrogen regulator protein. Under nitrogen-deficient conditions, the expression level of nblA, a gene required for adaption of the cells to N-deficent conditions, was low in a ΔrpoD4 mutant (<50% of wild-type), leading to complete loss of pigmentation after prolonged incubation. Regardless of the nitrogen availability, however, the mutant showed altered expression levels of a few genes related to cell division and showed abnormally elongated morphology, being about 10 times longer than the wild-type cells. These results indicated that RpoD4 takes part in adaptive response of the cells to N depletion as well as in regulation of cell division.
