Nitrogen source-dependent expression of a 126 kDa protein in the plasma membrane of the cyanobacterium Synechococcus PCC 7942.

The expression of a 126 kDa protein in the cytoplasmic membrane of Synechococcus PCC 7942 is shown to be dependent on the nitrogen source. It is absent in ammonium-grown cells and its quantity is inversely related to the concentration of nitrate or nitrite in the growth medium. Addition of ammonium-grown cells to a medium containing nitrate or l-methionine-dl-sulfoximine results in the expression of this protein. It is present in the plasmalemma of the Synechococcus NC3 mutant (nrtC gene deleted) and absent in the NA3 mutant (nrtABCD genes deleted). These results may suggest involvement of the 126 kDa protein in nitrate transport through Synechococcus cytoplasmic membrane.