Fig. 6. Ultrastructural localization of RNA polymerase I within A549 cells. Anti-RPI antibodies were revealed with fluoronanogold, followed by silver enhancement. After embedding, ultrathin sections (80 nm) were counterstained and observed with an electron microscope at 100 kV. The main nucleolar components are identified (FC, DFC and GC). A high density of particles is observed within the fibrillar components of the nucleolus. Bar, 0.5 µm.