Interaction of the intermediate filament protein vimentin with ribosomal subunits and ribosomal RNA in vitro.

If in a low ionic strength extract of Triton X-100-resistant residual cell structures derived from Ehrlich ascites tumour (EAT) cells Mg2+ was chelated by EDTA, vimentin became associated with unfolded ribosomal subunits. The first molecular characterization of this association has shown that (1) vimentin binds to the RNA moiety of the ribosomes, (2) vimentin has a higher affinity for unfolded small ribosomal subunits or 18S rRNA than for unfolded large ribosomal subunits or 28S rRNA, (3) the limited degradation of vimentin by the vimentin-specific, Ca2+-activated proteinase, with the formation of a 48 Kd breakdown product, abolishes its affinity for rRNA, (4) the association products are rather sensitive to moderate concentrations of KCl and Mg2+, and (5) reductive alkylation of vimentin with pyridoxal-5'-phosphate and NaBH4 has no effect on the affinity of vimentin for rRNA. Actin and tubulin do not interact with EAT cell rRNA under the above ionic conditions.