FIG. 4.
An rpoN mutation reduces the cellular level of nitrite reductase (NirS) and NO reductase (assayed as the NorB subunit). Cell extracts of strains MK21 (lanes 1), MK516 (lanes 2), and the complemented mutant MK516c (lanes 3), all induced for denitrification, were separated electrophoretically on a sodium dodecyl sulfate–12.5% polyacrylamide gel and blotted onto nitrocellulose, and the reductases were detected immunochemically. NarGH, nitrate reductase; NosZ, N2O reductase. Size markers (in kilodaltons) are indicated to the left of each panel.