Fig. 4. Electron microscopic analysis of ptr11-1. The ptr11-1 cells were cultured at 37°C for 4 hours, fixed and embedded in Quetol-651. Thin sections were examined under an electron microscope. Part of a cut phenotype cell with the cleaved nuclei is shown. Arrowheads denote electron-dense materials. No, the nucleolus. Bar, 1 µm.