Fig. 6. The influence of the CxxM motif on the formation of intranuclear membranes. (A-D) Electron micrographs of ultrathin sections through microinjected Xenopus A6 cells expressing Xenopus lamin B2 mutant B2-SxxM (A,B) and Drosophila lamin mutant C-CxxM (C,D). (A,B) Nuclei of cells expressing mutant lamin B2-SxxM contain proteinaceous aggregates that are associated with the nuclear envelope (asterisks) but no intranuclear membranes. (C,D) Protrusions in the nuclear envelope (arrows) are seen in cells expressing the lamin C-CxxM mutant. The protrusions are filled with protein aggregates similar in electron density to those formed by Drosophila lamin C (see Fig. 4E). A pore complex is indicated with an arrowhead in B. cy, cytoplasm; no, nucleolus. Bars, 1 µm (A,C); 500 nm (B,D).