| Abstract: | The binding of the intermediate filament protein vimentin to a variety of naturally occurring RNAs and DNAs was studied. The relative capacities of the various nucleic acids to associate with pure 3H]vimentin were determined in competition experiments with 28 S rRNA from Ehrlich ascites tumor cells. The reaction products were analyzed by sucrose gradient centrifugation at low ionic strength and in the presence of EDTA. Under these ionic conditions, vimentin reacted preferentially with single-stranded nucleic acids, particularly with those of high (G + C) content. The vimentin binding potentials of single-stranded RNAs and DNAs were largely comparable. However, when the concentrations of mono- and divalent cations were raised to physiological and higher values, only single-stranded DNA retained its vimentin binding capacity. With increasing KCl concentrations at 0 to 1 mM Mg2+, increasing amounts of vimentin were detected in complexes which sedimented considerably faster than the bulk of the DNA, suggesting cooperative binding of vimentin. The salt optimum of this cooperativity was at 200 mM KCl. Thus, the capability of vimentin to discriminate between single-stranded RNA and DNA under physiological ionic conditions points to specificity of the interaction of vimentin with nucleic acids. |
