Polyribosomes are not associated with vimentin-type intermediate filaments in Ehrlich ascites tumor cells

Polyribosomes were isolated from Mg2-stabilized, Triton X-100-resistant residual cell structures and from a postmitochondrial supernatant of hypotonically swollen and homogenized Ehrlich ascites tumor cells and analysed for their vimentin contents by polyacrylamide gradient slab gel electrophoresis. Whereas polyribosomes from detergent-resistant cell residues were accompanied by a small amount of vimentin on sucrose gradients, polyribosomes isolated from a hypotonic, postmitochondrial supernatant were free of vimentin. Since the presence of vimentin in cell residue-derived polyribosomes might be interpreted as the result of unspecific adsorption or cosedimentation of vimentin filament fragments, both due to the presence of high Mg2 concentration during cell extraction, the results suggest that there is no direct and stable interaction of polyribosomes with vimentin-type intermediate filaments in suspension-grown Ehrlich ascites tumor cells. This is in accordance with the electron microscopic observation that cytoplasmic regions rich in intermediate filaments are virtually devoid of polyribosomes. When the extraction of the same cells with Triton X-100 was carried out at low ionic strength and in the presence of small amounts of Ca2, residual cell structures were completely destabilized and clean nuclei without any attached cytoplasmic material were obtained. This is due to the degradation of the vimentin-type filaments by the Ca2-activated thiol proteinase highly specific for vimentin.