Figure 4.

Microinjection of the mixture of vimentin cleavage products produced in vitro by the action of HIV-1 PR or a defined vimentin peptide encompassing the entire amino-terminal head domain into SW 13 [vimentin⁻] cells also produces nuclear chromatin condensation and redistribution, but has no effect on nuclear shape. CLS microscopy optical sections of the chromatin distribution of a cell microinjected with HIV-1 PR (7 μg/ml) as a control (A) and a cell microinjected with a mixture of vimentin cleavage products (produced from overnight digestion of vimentin at 0.2 mg/ml) (B) demonstrate that the vimentin peptides, and not the HIV-1 PR, are directly responsible for the nuclear effects. Microinjection of the isolated amino-terminal peptide of mouse vimentin, NT 1 (vimentin residues 1–96), into SW 13 [vimentin⁻] cells resulted in nuclear alterations (C), similar to those seen with the vimentin cleavage product mixture or in SW 13 T3 M [vimentin⁺] cells injected with HIV-1 PR (Figure 2). Microinjection of NT 1 into SW 13 T3 M [vimentin⁺] cells and incubation for 30 min at 37°C also resulted in condensation of chromatin and alteration in nuclear shape (D) and a perturbation of the vimentin IF network (our unpublished results). Injected cells were incubated for 30 min at 37°C before fixation, staining with propidium iodide and preparation for CLS microscopy. Bar, 10 μm (A–D).