Interaction in vitro of Non-Epithelial Intermediate Filament Proteins with Histones

Abstract Non-epithelial intermediate filament (IF) subunit proteins show a high and specific affinity for core histones at physiological ionic strength. When IF proteins are titrated with a mixture of core histones and linker histone H1, in general the latter is totally excluded from com plexation and in the adducts formed the moderately-arginine-rich histones H2A and H2B are progressively replaced by the very-arginine-rich histones H3 and H4. At histone saturation, 2 molecules of nonneuronal IF protein bind 1 histone HI molecule or 8 core histone m olecules, whereas due to its glutamic acid rich, C terminal extensions one dimer of thp 68 kD npnrofilament nrotein associates with 3 molecules of histone H1 or 24 molecules of core histones. The salt stability of the insoluble association products is dependent on the amount and arginine content of the constituent histone species. Rem oval of the non-α-helical N- and C-terminal polypeptides from IF proteins by partial chymotryptic digestion does not affect their histone-binding characteristics. Since core histones are only partially inactivated by limited tryptic digestion, they also appear to react through their a-helix-rich central domains; the limit peptide derived from histone H1 is com pletely inactive at physiological ionic strength. Affinity chromatography of rod domains of IF proteins on core histone-Sepharose 4B and of histones and their limit peptides on vim entin-Sepharose 4B has shown that the interactions involving fractions of histones H3 and H4 are extrem ely resistant to salt and can be dissociated only with arginine or salt under denaturing conditions. In general, the experim ental results revealed close parallels between the association of histones with IF proteins and their interaction with DNA.