EFFECT OF THE IONIC ENVIRONMENT ON THE INCORPORATION OF THE INTERMEDIATE-SIZED FILAMENT PROTEIN VIMENTIN INTO RESIDUAL CELL STRUCTURES UPON TREATMENT OF EHRLICH

Ehrlich ascites tumour cells, propagated in suspension culture, were extracted with Triton X-100 under different ionic conditions to study the sensitivity of intermediate-sized filaments formed in vivo to changes in the ionic environment in vitro. The following results were obtained: (1) in solution of low ionic strength and in the absence of di- and polyvalent cations, vimentin was quantitatively solubilized and recovered from the postnuclear supernatant by precipitation with (NH4)tSO4 (23 % saturation) or spermidine (2 IBM). (2) When the cells were extracted in low ionic strength buffer in the presence of 4 mM-Mg-acetate or 1-2 mM-spermidine, vimentin was quantitatively incorporated into Triton X-ioo-resistant residual cell structures. It could be easily extracted from Mgl+-stabilized cell residues with Mgl+- and polyamine-free buffer of low salt concentration; spermidine-stabilized cell residues were very resistant to dissociation. (3) In a solution of high salt concentration and in the absence of di- and polyvalent cations, little or no vimentin was retained in residual cell structures. Better, though not quanti-tative, binding was observed in solution at physiological NaCl or KC1 concentrations. (4) A synergistic effect of mono- and di- or polyvalent cations on the association of vimentin with the nuclei was detected when the extraction of cells was performed at concentrations of these ions